SVTF the analogy was exactly right. He couldn't see that the volume varied by temp and it does. The analogy proved "the volume changes are driven by the temperature change" just as you said.
You are exactly right as to net effect of the temp change on the pressure and flow which is why you have to resize the turbine. It really is as simple as sizing for the flow you have whether it is a cold/hot flow or large/small engine. The turbo doesn't care where it's located or what engine it's located on, all it cares about is flow.
Extra heat = more pressure = more flow = more work out of the same number of molecules of gas, so you won't get as much total boost out of a cold system as a hot system. Maybe you can only get a max of 24# of boost of a colder system while you could get 32# of boost out of a hot system. That only means if you are going for max HP then go hot, but if you are going for normal boost levels you can get that out of a colder system. You can't argue with the fact it's working for STS and others.
The turbo works with any kind of flow but YOU care about whether it is flowing enough to give you the performance you want in the portion of the powerband you want it. Which comes back down to proper sizing for the situation you have. The bottom line is that you need the proper sized turbine for the flow you have.
The main issue with the rear turbo is that all the formulas are set up for a hot/close to the engine turbo so if you go rear you have to experiment or do a lot of math. In any case picking the right hot and cold sizes is always a bit of hit and miss, but with a traditional set up you have people you can copy.
There is also the oiling issue. Some turbos don't require oiling and the fact that you are not in the high heat environment of the underhood it means oiling (and coking) is less of an issue. STS uses a reservoir and small pump which has the advantage of compactness and cooler oil temps. I've seen some that run a line up to the engine oil.
