One other thing to consider... the basic premise is flawed.
I have never seen a delay/line AFTER screening of anything more than a few seconds. Even then it is just because screening is moving things along and several bins are coming out quickly.
If there is a delay pre-screening, it is because security has not moved the mound of bins waiting to be moved. And no amount of passenger stacking of bins will change that.
So the idea of stacking/not stacking having a material effect on wait lines seems false.