This'll get a bit more involved -and probably makes some people's eyes glaze over...
When the exhaust valves open there is a pressure wave that exits the cylinder most of the increased pressure in the cylinder is lost very fast, in fact the pressure should be slightly negative in the cylinder as it expands and the intake ports at the bottom of the stroke are revealed. The hot exhaust gasses leaving the cylinder through the head are still expanding a bit and cooling as a result of the expansion, but the majority of the cooler air entering the cylinder is not mixing with the hot combustion gasses, rather it's pushing the exhaust gasses out of the cylinder volume. For the sake of some simplicity, think of the hot combustion gasses and cold intake air as water and oil. You are merely displacing the oil which floats on top of the water out of the cylinder (this is the over-simplified elementary school demo, and is intended to illustrate the principal rather than explain how varying density and temperature media interacts at the interface front).
I'm not clear on what you are asking about the heat retention pre-turbo... Are you asking before the compressor or before the power turbine (just guessing the latter). As the exhaust gasses leave the cylinder, you want less of that heat to be absorbed into the walls of the exhaust passageways, and more of it contained in the gas itself. If you've ever let the air out of an air compressor, you'll note that it is cool or cold, this is an effect quantified by the Gay-Lussac gas law. Molecules running into each to other makes heat (like friction), so squeezing molecules closer together makes heat (since molecules can run into each other easier due to proximity). Cooling a compressed gas then reducing the pressure of that gas will cause molecules to spread out and not run into each other, and this cools the medium down. By the same effect, heating a gas which was at room temperature and ambient pressure (in a confined space), will cause the pressure to go up - this effect can be witnessed by putting a closed Tupper-ware in the microwave and watching the top blow off. The reverse is done in food packaging to "vacuum seal" food - it's heated well above room temp at ambient pressure, then a lid is put on and the food product is allowed to cool, this reduces the pressure in the container. By that last example, that is the effect you don't want to have happen mid-traversal of the exhaust header, and manifold - you want all of that pressure and heat (both interrelated) to appear at its earliest convenience at the fins of the power turbine, at as close the the exit pressure and temperature of the cylinder. This will provide the maximum amount of energy transfer to the fins of the power turbine as the gasses expand out to an un-constrained volume of the exhaust system and muffler (i.e. vent to open air). By the same measure, you don't want heat transfer from the hot side of the turbo to the cold side of the turbo, since that would heat the intake air at ambient pressure, which would make it act more like a spring than a fluid since it would want to spread out more (think of this like "vapor lock" for air).
In an efficient engine, you aren't spending a lot of time mixing things, rather it's better to segregate the gasses completely if possible. This is the reason for the move from 2-stroke to 4-stroke - it is more efficient, and easier to control how the gasses behave, since you can completely change the volume of air with very little interaction due to the addition of two distinct cycles (intake and exhaust). Greater separation allows for other systems like EGR to have simple expectations, so their design is easier. This also doubles the time per full cycle traversal (since there are twice as many), so it makes things like computer control easier. Software designers like their problems simple and constrained, especially on cheap hardware.
Higher fuel pressure means that you will be able to push more volume of fuel into the cylinder, electronic injectors do give you added control of timing and in some cases the ability to do multiple injections. In the first case, yes you are getting more fuel into the cylinder, but you can already do that with larger injectors (try the G90 injectors for the 8V92, that's 90cc of diesel per stroke). Good electronic control and higher popping pressure of the injector means that you get tighter control of the combustion timing, this again is great for software engineers since the equations they use to control the air-fuel mixture gets easier when there aren't uncontrolled variables. The ability to do more than one injection per power stroke helps keep the flame front from coming in contact with the piston (good for reliability), allows for internal shock-waves within the cylinder to mix the air so the likelihood of complete combustion is higher (lower emissions), keeps the combustion temperature lower (lower emissions, less heat soak), and actually makes the engine quieter (10x of .22 caliber rifle shots are a lot quieter than one .50 cal shot). Finer spray pattern also lets the air mix with the fuel - the term you are looking for here is "atomization", basically you want the fuel to mix with the combustion air at the correct air-fuel ratio, but also do so down to the molecular level.
This is beyond the design of a 2-stroke though - I think patracy had a thread in conversations about making things too complicated, really the DDEC systems are not great because they are trying to solve a problem that you really need a 4-stroke with. I'm in agreement with patracy about over complicating this if you're trying to add a system like DDEC or roll your own to a MUI 2-stroke - really what you want in that case is a modern 4-stroke that was designed that way
That said, by doing the simple things like keeping the air filter restriction low, and the exhaust back-pressure low, you will notice reasonable gain in performance, properly sizing the engine, turbo, injectors and radiator/intercooler will help too.