The key to the biggest flares is 1) building up a lot of total speed, and 2) efficiently converting that into a flare. This is an example of a huge flare with 314ft of altitude gain:
I think it's most useful to look at the speed polar:
What this shows is (1) building up a huge amount of speed by diving aggressively. (2) continuing to dive but increasing the horizontal component of velocity. (3) as smoothly as possible exchange airspeed for lift. (3) begin going up. (4) maximum upward velocity 45 mph. (5) top of the flare, when vertical velocity hits zero.
If you flare too hard, or if you break it up into "phases" between 2/3/4, you will lose more energy and not gain as much altitude. Also if you flare too gradually, you will bleed off speed due to drag and not gain as much altitude. It's a balance.
Interestingly on this track, (2) has more total speed than (1). I actually think it should be more efficient to not go quite as vertical as that jump, and short cut the transition from 1 to 2. The main thing is to maximize total speed before the flare, but if you can do the same total speed at 1:1 glide as when vertical, then you're in a better position to start the flare.