I've never tried putting my unlit on the bottom. Is that working better than putting it on top of the lit then waiting for it to all get going? I guess my fear is that it would burn too dirty, but since you are using Weber Briquettes that probably isn't the case.
I have been doing it this way as long as I can remember. I let the coals heat up the oven for at least 30 minutes, so there is no dirty smoke, even using other brands of briquettes. I've used Coshell, Stubb's, Royal Oak from Home Depot and now the Weber briquettes. I haven't used KBB, as I think the ash build-up "could" cause it to not get as hot as I'd like.