Replying to Question about Mounting

So, this summer I bought a pair of on3p j-mo's. The kid said they had been center mounted with FKSs to 28.5s. When they arrived, they were certainly centered, but I couldn't quite fit my 28.5 dalbellos in. After fucking around with the forward pressure on the heelpiece and maximizing the size of the fit (if you've ever played around with FKSs you'll know what I mean) they still wouldn't fit safely (with the white piece aligned to the line on the heelpiece). Is there any other option to mess around with before trying a remount? They're oh so close to fitting... I think the kid had a radically different bsl or something.

thanks yall