It's possible that the subs were still producing the low end but were aligned so well that it seemed to come from the mids which is what u want.
I think, sometimes, people expect too much from their mids and forget that the sub is there to reproduce the low end for you. There's absolutely no harm done by using your sub even in an sq build. The only issue is preventing the subs from being localized, with proper phase alignment, this can be achieved. FWIW, I used to try to run my mids super low for a full sound too....while they'd play it, they had no authority. So, I put the xover point at about 63hz 24db slope and same for my subs and got them properly aligned and the difference was day and night.
It may seem cool to have mids playing down to 40 or 50 hz, but If it doesn't sound good, you've missed the point. You've gotta find what works best for your equipment, and in my experience with BA PROs and even way better mids, you likely won't get subwoofer-like authority from your front mids....so make the sub do its job.