um, just to clarify, isobaric is where you use one driver to "load" the cone of another driver, effectively almost adding the vas, or equivelant air pressure compression of 2 cones to one cone. there are different ways to set it up, like side x side with shared space inverted phase(planar) or firing one at the back of another, but inverting one can allow you to minimize the airspace between the 2, and decrease efficiency loss. one effect of inverting, is that the basket/motor, along with cone shape, can interrupt cone noise, or "sound" wave coming from the front of the cone, and it will operate on mostly air compression waves. and, then there is also the cooling factor. especially with small sealed enclosures, the coil has access to cooler air if played at high levels for extended periods. really, i have not seen, or experienced anyone choosing to invert on these principals, just for the 2 reasons that everyone has already stated. looks, and clearance. sub displacement is also a bit of a factor, but really only makes a little difference on smaller enclosures, and large motors/deep cones. also, to answer your other question about phase, yes, the sub will be moving in the opposite direction, since it will face the opposite direction, so, if you have more than one, the inverted one(s) should be reversed in phase, or there will be cancellation. if it is single, or they are all firing into the enclosure inverted, then phase does not need to change.