Fish go strait, unless you go super short.
RNF huh? I take it it's the Lost Round Nose Fish? go with the thruster set up over the quad set up (for the love of God dont use all 5) it'll keep you a little more loose in the tail. The reason the fish will prob be more responsive is that its shorter. In actuality (and because you're surfing such big waves) you should probably be using a shorter short rather than a fish (unless those same head highs you are riding are pure mush?) Check out a Lost SD2 or even a Lost Shark- both have the same short charectaristics you're used to, but have a little more thickness so you can plow through mush and solids alike and go shorter length.
Ive given you the info, so now it's your turn: where are these head highs at you usually surf?