Perhaps it was necessary to limit this ability's total healing with a cool down, but there is one major flaw with it. Abilities like lightning form and others that do damage over time tend to steal the surge heal procs most of the time, resulting in very minor healing and preventing hard hitting abilities from doing any healing on crits.
I am unsure what the cool down time currently is, but for the sake of this proposal I will assume it is 0.5 seconds. My idea is that, each 0.5 second interval, the system takes the single largest crit number done in that time and heals the player based on it. Essentially, the heals will be set on fixed 0.5 second intervals as long as the player is landing crits, but the high damage crits between those intervals will not go ignored. AoEs should be included, and in their case the total crit damage done to all mobs from a single cast is what would be counted.