Hi everyone! Thanks for the awesome responses!
Sorry about the confusion when I mentioned he's a "fat boy", I actually meant "fat boy at heart". He's definitely not a fat boy physically lol. He is quite healthy for his size, according to our reptile vet. Nearing 4 ft. and now at 1300g+. No space between his scales, and definitely doesn't have the chunky/scales-are-too-tight-on-him look. He's also no more than 2 yrs. old.
I'll definitely just shy away from feeding him in the next few days and wait until next Tuesday to feed him again (since it'll exactly be 7 days from when I fed him). Also, if I do see him really obviously tailing my heat signature, like Reinz's BP, and getting into his "strike" pose more often than not, as though he's ready to eat, I may just give in and provide him another medium rat.
Also, thanks for letting me know about the 15% rule being obsolete to adult BPs! I've been weighing my rats for him and wanted to make sure everything matched his needs. I guess I will just go on with eyeing the biggest part of his body and go from there from here on out. At this rate, my supplier's medium rats (avg. 100-110g) are definitely too small for him. I fed him a large rat the other week to see if he could take it and he was in his hide for the next 48 hours. Not a single sight from the "fatty". No regurg, just a "happy" night-roaming snake 4 days later. I guess that means large rats will keep him content.