I don't really know! LOL
I've been messing around with the crossover settings and it seems I can get more bass / boom out of the sub when it is at 100Hz, which is desireable at schools. For weddings, the tops are usually closer to the dance floor and sound fuller at 80Hz and not so 'in your face'. I don't really need the extra boom at weddings, just some nice bass. I just DJ'd a wedding at the place in the photo (stock photo, not my wedding) and I had one FBT 4a on each side of the stage. I used only one RCF Art-705AS holding up one of the 4a's with a pole mount, the other was on a tripod. The crossover was at 100Hz since the tops were far away from the dance floor, they had to shoot over the head table. The sound was awesome, tons of bass all around the dance floor.
I've used the RCF sub in quite a few different venues now and I can tell you that placement does make a difference. I have used
one 705 in a smaller hall (holds 125)
http://www.musicmaestro.net/photos8.jpg and had little bass on the dance floor, it was somehow cancelling itself out. The sub was set up off to one side about 10 feet in from the outside wall. Next time I was at the same hall, I was able to set the sub up against the wall directly in front of the dance floor and it was great! When I use a single sub for 4 or 5 hundered middle school kids, I set it out in front of me and the sound is awesome in a gym. Check out this hall, it is HUGE!
http://www.musicmaestro.net/Italian_Ctr_head_table_web.JPG If you look closely, you'll see the edge of my single 705 sub, it sounded great that night. It really depends where you place your sub. Unfortunately, with most of our typical wedding set-ups, we don't have the time or available space to be very fussy in that regard, which is unfortunate.