If you put it in the lower part of the oven, it will pre-heat a bit faster, but you want it close to the broiler so that you can broil the pizza as it bakes.
As far as enhancing the pre-heat temp of the stone using the broiler, you have to be close- really close. At least, that's been my experience. I tried augmenting the pre-heat of a 1/2" cordierite stone with broiling and a 4" gap and the results were pretty much imperceptible. If you look at the nearlypolitan thread (where they really drive up the pre-heat temp of the stone), they work with a 2.5" gap. If you're just getting started, a 2.5" gap is going to be really hard to work with.
Soapstone is quite a bit darker than cordierite, so it should absorb radiant heat better. I think a 4" gap might give you a bump with broiling, but, to start, I'd go easy on yourself and go with 6". Once you can launch a pie with your eyes closed, then I'd narrow the gap. Soapstone @ 550 (without a broil pre-heat) can do a 3.5 minute pie. 3.5 minutes is just on the edge of the elite spectrum. As I mentioned before, that's a relatively even colored Lombardi's offering. Master that first and then close the gap and move into a more traditional splotchy charred elite style.