Originally Posted by ThermionicScott

It's one of those things where it's fine if you know what you're doing. But sometimes we can tell a poster is in over their head and doesn't really appreciate derailleur capacity, or remembering not to use certain gear combinations, so the simplest and I'd argue most responsible thing is to say "no, don't do that."

Because I do club rides and long brevets that impair my cognitive abilities, I include myself in both the "clever" and "idiot" categories. Toward the end of a 1200k, I don't want to have to remember not to use the extreme gear positions, because that's when I'd accidentally shift into them and blow up my bike. So my drivetrains are set up so that any gear combination works (chain rubbing on the FD cage is non-fatal, so counts as "working" here.) If I need wide enough range, I'll suck it up and install a long-cage rear derailleur. My Deore 7-speed ones shift just fine.

One idea that comes to mind for squeezing more capacity out of a short-cage RD is to install larger pulleys. After all, that's how the big 3 are doing it. You might have to bend derailleur cage tabs out of the way -- or remove them entirely. (EDIT: in the long time it took me to compose this post, you already got to the larger pulleys idea. )