Flip is at a point now that he won't gain too much from improving his approach. He was far away from this point in the past but improved I'd say dramatically (this is not a big word by any means - it's real) in the last week or so. You really need to "power" yourself in a two-leg jump. Obviously, you need great movement efficiency and strength to prevent your knees from collapsing if you do it though.
I could try the same thing Flip did and my knees would collapse and mess my jump up.

So at this point, besides some better approach (a bit more speed under control if anything) - he's going to be limited by maximal strength. Increase that and Flip will dunk in games on the regular rim no problems.