JimL,
Some experience in this stuff has lead me to believe that zero exposure landback distance (or the deck-to-tail clearance distance), is driven by the OEI power ratio, where the machine has to have enough engine power to be somewhere between IGE and OGE while OEI. (love those acronyms!)
The takeoff is always the tough part, requiring the most power ratio, as the aircraft is crawling up from a zero speed, zero altitude energy well. The landing is much easier, because the kinetic energy and potential energy both provide equivilent power to lend a helping hand.
Rotor inertia is a nice contributer, too.
I have some influence plots to illustrate this on my other computer, and will try to post a tome on it in a bit.
SFC, excess Power ratio, engine and transmission weights, and cruise fuel burn conspire to make us limit the OEI performance. There are ways to make it different, but they will wait until engine technology creates the true "burnout rating."
Gomer has my vote, gas, and the range/time that it brings, are much more important to flight safety than OEI engine.