Two hours in foil at 250° for spares is quite long-- they should be already falling apart when you unfoil them. It would be even worse on smaller loinbacks. If you're measuring 250° at the dome, then your top grate temps are going to be more like 225-235°, so that may be why it's worked for you previously. All things considered, I'd limit loinbacks to about 45 minutes in foil at 250°, measured at the grate. Stogie's method calls for 2.5 hours in foil, but strictly at 225° at the grate-- I use it; it works.