The problem (in my experience) isn't the chance of getting a trance, it's reaching orgasm in the first place. Humanity should be extinct in LR2 universe given the fact that sex is apparently the most physically exhausting task in existence
I agree it's ridiculous to become exhausted by things like fingering or kissing. Also, why should fucking ehaust your fingers, and why should fingering exhaust your dick? The exhausting factor is there to limit how much you can make a girl cum in one session.
My suggestion would be to make it possible to start things like fingering, kissing, groping etc. which don't involve MCs dick any time as often as you want and as long as you want, but make the arousal gain of the girl be dependent from MCs remaining energy. So to say, a percentage factor, starting at 100% arousal gain in the first round and 0% when MC has no energy left. The same way chances should increase for a dick failure at lower energy levels, rather than it being a hard limit at 0 and having zero impact on your boner at 1 to 100% energy.
Second thing I'd change would be that changing position should *gain* you some energy rather than the 5 points energy loss. If you do something new, you do it because what you are currently doing is boring or exhausting you, so any change would be a win.