Is there a slope angle range which is conducive to balls plugging in the faces of greenside bunkers? That architects should avoid using?
Pete,
My answer would be the same as Joe H's. I think it has more to do with sand quality, specifically, roundish particles tend towards buried and fried egg lies more than a sand with rectangular particles. There are also grades like "sub-rounded" that are halfway in between.
The USGA has a "penetrometer" test with values that equate to firm through "tend to bury" to help choose sand. However, in general, steeper slopes tend to lead to more plugged lies.
I bet many areas are similar to Texas - local sands are cheap, but rounded particles, and good angled sand must be trucked in from other areas at great expense, with the price differences up at $30 per ton for local, and $90-$120 for the angled sand, usually really white. If your course has pluggy sand, it's probably a value decision.
BTW, all sands (and soils) have their own natural "angle of repose" i.e., the steepest angle sand will stand in a pile. Even when using Better Billy Bunker, they suggest bunker slopes no greater than 80% of that angle of repose, and if your bunkers have no liners, it would probably be best to be even flatter.