The H\V diagram applies to the case where full climbing power is applied. The shape of the avoid curve (if there was one) would be completely different for the approach case. If you fly a constant angle approach (about 6-8 degrees) at a constantly reducing airspeed, ie the constant apparent groundspeed technique, you will always be able to make a reasonable EOL from an engine failure anywhere on the approach, PROVIDING THE LEVER IS LOWERED QUICKLY ENOUGH (even in an R22), until you get close to the hover; then hover EOL technique applies.
Unfortunately the above technique puts you in the environmentally unfriendly blade slap condition in most helicopters for a substantial part of the approach. Keeping the speed up a bit then flaring gently obviates this somewhat.
The dangers of a engine failure on the approach (like you have forgotten the carb heat) are that when using either technique, the cues of sudden yaw and lowering RRPM are much less obvious. If the speed is low, RRPM recover very slowly and flaring is not an option since you need to preserve airflow through the disc.