You might try no foiling/wrapping at all for a heavier bark......
In that case, just dab on the sauce later in the cook, in several layers to build up to how thick you would like......
The foil will braise the piece and soften the bark buildup, so maybe experiment around a bit without.....
I often do loin backs cooked in foil first, then set out on the grate, saving the sauce/ juice in the foil wrap to carefully pour over the racks several times, maybe ten - fifteen minutes apart, letting it set each time.....building upon the initial bark.......messy, but it works great!!
I Aim to get a little short of "fall off bones" and aim for a good clean " bite off the bone"