As far as I know you’ve always been able to overlap.
At some point, several versions back, they made it such that you get a red warning when any portion of two models overlap. It wasn’t 100% perfect and sometimes you could squeeze in a touch of overlap without triggering it red, or trigger the warning prematurely when the models were too close but not actually making contact (as if it were using simplified “bounding box” shapes that weren’t entirely precise).
But you could always override or ignore the warning, and send the print anyway. In fact, when printing sets of many individual small parts, I often find it extremely handy to intentionally overlap the rafts slightly, in order to merge them into groups which makes removal so much quicker and easier.
I notice on the latest version the red warning pops up as soon as the rafts touch, even if the models themselves aren’t touching. Not sure if this was intentional.
But I assume you can still ignore it and send the prints anyway?
EDIT: Here’s an example from Preform 2.20. The rafts overlap. The minions aren’t quite touching in either, but in the bottom picture I moved one just a small nudge closer to the other (by a few pixels). Based on the original post I assume that was also the behavior in 3.8.0.
In Preform 3.8.1 the warning occurs as soon as the rafts touch.