IS THERE A CAP ON THE NUMBER OF DISPOSITIONS PER YEAR PER ALJ?

Yes

CONGRESS SEEMS TO THINK THAT THE HIGHER THE DISPOSITION RATES AF AN ALJ, THE HIGHER THE ALLOWANCE RATES, SO WHAT IS THE CAP?

The cap is 720/year. Once an ALJ decides 720 cases, he or she can just go fishing. Unfortunately, there are systemic problems with keeping an active and effective list of ALJs and qualified candidates, so with a cap at 720, it looks like the backlog of which I wrote recently will continue into the forseable future.