Importance of rear trapping and acoustic foam questions.

[yoga]

I have double doors on the rear of my room but I placed bass traps on all four corners and first reflections. How important is that rear trapping?

I couldn't afford to make any more bass traps, so what I did with sheets of 2 and 4 inch foam was to space it from the walls by 4 inches. Will that lower the frequency absorbption of the foam or it's properties or was it a foolish thing to do?

I also did some layers and tying up of foams into tubes. Will that turn the absorption properties lower and maybe turn them into low absorption foams?