Using the actual shape of the model to calculate will need a lot resources in computer to process and take a lot extra time. So using standard shape of bounding box instead is a compromis at the moment till we find a more balance way to use the actual shape and not crash the software at the same time.
I understand, but... auto arrange models will failed in most of cases (yes, IM has a big problem with placing models in build area), me as user try to do it manually, but I check drawn restricted area by IM to do it. And after that, I get slap form IM, that still something is still incorrect, because IM will check different restricted area, that user see. And we don't know even on each model we have problem. If someone prints only some boxes - it's not a problem, drawn restricted area is correct. But printing circles, or angles models, we have big problem.
From me perspective, should be only "soft check", so we get message, that something can hit printer head, user take responsibility on him, and IM continue process; instead of "hard check", and interrupt process as is now.