It has to capture it on a relative basis.
The problem I have with Tascam is that it loses the room ambience
Yes, to some degree you are right but if the losses are too signficant I would argue it will bias a relative discussion as well.
I don't find the Tascam I have loses much of the room ambience at all...if anything it seems too sensitive to background noise often times and makes it seem a bit worse on the recording than in real life.