Depends on the driver and XO point/slope. The older frames are a pain to mount from the front due to having to make all the notches to clear their stiffening ribs, so rear mounting is the norm.

Due to the nature of a horn's dispersion and Altecs generally having XO point/slopes that have long WLs compared to flange thickness, flush mounting looks nice, but acoustically moot. Rear mounting does screw a bit with the standing waves that propagate across both the driver and baffle, so there will be some very minor response smoothing if the baffle cutout is heavily rounded over, but it's a hassle working around the mounting hardware, ergo unless you use a clamping or other mounting system it's not considered worth it.

GM