When you do go to a larger screen, one that produces all the more wider a light source, then the reflections off the ceiling (...and the reduction thereof...) will become all the more important.
DIY paint coatings can offer up just as much retro-reflective properties as a BD Screen. The truth is, it's just not pursued much because most of us feel that the caveats that acco0mpany such screens outweigh the benefits. Graininess....loss of viewing cone (reduction of off-center brightness) are things many like to point a finger at DIY Screens for possessing, calling such detrimental...or outright "Bad".
This is because DIY Screens can in fact be so "Good" that anything that is "less than good" that is added into the equation gets all the negative press.
However, to counter that point, it's obvious that there are many who are willing to accept such things as being necessary because the supposed caveats are actually "solutions" to prevailing issues many must deal with, such a highly reflective walls and ceilings in very close proximity to the screen.
If you want a high gain Gray DIY Solution that will get you well into BD territory, look at these images.
A SF v2.5 HG -6.0
sample laid directly against a SF v2.1
The Screen is being inundated by 2 100 watt Floods positioned directly overhead.
Obviously, it can be done. But there is a appreciable loss of brightness beyond a 40 degree "off axis" position. And there is a degree of graininess that matches that ...but does not exceed that of a BD 1.4 screen