St Louis cut pork ribs on dry side

KB

I cooked some St Louis style ribs that I bought on sale for $1.99/lb. They had been previously frozen, and had about 12% water injected in them. I thought I'd try them cause I usually pay that much for regular spare ribs.

I cooked them using Perry Lang's method of 4 hours indirect at 250 deg, and then 1-1/2 in foil, followed by a short time back on the grill.

These ribs are somewhat drier than the previous ones using regular spare ribs and the same recipe. Was it the cut, the meat, or perhaps because I changed something in my cooking? This time I used a rib rack to hold them; last time they were placed directly on the grid. Last time, the meat was practically falling off the bone; the St Louis ribs were quite tasty, but the meat was a little more chewy. It would be nice to be able to replicate the same taste/outcome each time if I follow the same procedure.

Any suggestions?