I think for most of us, the goal at BI and probation for that matter was to not stick out. So the middle ground as far as dress goes, would be slacks/nice chinos and a button up shirt.

on the more formal end, some dudes wore suits/sport coats all the way through BI, and on the informal end, some guys wore khakis and polos. The women in my class (all 2) erred on the more formal side...But I have no idea what the equivalent would be for feminine clothing

once you get to sim, on probation I’d be conservative and avoid jeans or non-collared shirts, but khakis and a polo would be completely normal