While I can understand how someone might come to the conclusion that the foot bed would work just as well under the liner, it gives the effect of wearing very thick socks. It will probably feel more snug because everything doesn't fit as neatly as it should and is taking up volume. I have read threads at other sites claiming this too. The fit might be improved because his boots are too big. Just guessing. He said the fit was better but was the control?
I believe anything under the liner would only address gross alignment (heel/toe lifts) and under the foot should be fine alignment. I think I would go without a foot bed before I would put it under the liner. I'm not sure that is correct but fine movements comes from the foot and not the liner.
I also think that if there was real benefit to this, boot fitters would be doing it because they would be able to charge close to the same but be done way quicker.