Not an expert by a long shot, but my spans are 1/8" less than that. Basically I had them shortened time after time until the pain went away. However, one of my balls has just about that same span and I can throw it all day, so go figure. In other words, your span is good enough, but (IMHO) not perfect.
As Vini implies, a long span could cause your thumb to get a callus on the knuckle as it bends to fit into the hole.
Also, the pitch of the thumbhole affects the proper span. I have balls of 0, 1/8 rev, and 3/16 rev. The ones with reverse pitch can be a tad longer. Of course I have to throw each pitch differently, so I have to make a mental note of which one I'm throwing. Just to spice things up, I have a set of 0-pitch IT slugs and a set of 1/8 pitch, so I can actually go from 0 to 5/16 pitch if I want to. Very confusing at times, but that's what gives me joy, so... whatever....
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