The various answers on possible power loss come from the original dogbone body's flat top and the too-low internal clearance from air cleaner body to the carb inlet. By adding a 1/2" (or more) ring spacer, the clearance is then such that air can better make the 90 degree turn into the carb mouth. Same thing happens to a std air cleaner with a non-sculptured top & too little carb clearance.
Without a riser as originally built, there was often as much as a 40 bhp drop on a dyno. Second, there were at least three manufacturers of these things and no one's compared the internal clearance on all three, to my knowledge. The original dyno tests kind of killed the market for Panteras, even though a simple ring spacer later corrected the problem. I've seen a couple of high-horse Panteras with the engine screen cut out around a taller dogbone.