I have had this problem with various shorts, despite using a Brooks B-17. I find that the short pads bunch up just below the perineum and cause compression. My solution, which has worked, has been to make a small slit in the interior material, then use long, narrow scissors to excise a length of pad about two inches long and half an inch wide from the pad. This effectively creates a notch in the pad and prevents bunching. It works. You can patch the small slit with a piece of iron-on tape. Why manufacturers do not pre-mold shorts pads with this in mind is beyond me.
Another approach is to buy a saddle with a recessed hollow in the same area. Selle makes an An-atomica; you can also buy a Brooks with a slit in the leather:
http://www.mcmwin.com/saddle%20shop.htm