Thanks guys. The most common mistakes: Sometimes I don't pop (enough), then they just ghost rocket; sometimes I don't flick (enough), then they only turn half. I know how to set up my feet, I know I have to pop and only flick later. I guess a lot of it is really psychological: the more I dread the heelflip part of my session, the less likely I am to make any progress. I've been wondering if I should just skip that part for a week and see what happens.
Since we're doing heelflip tips now, here's a little hack that helped me learn heelflips 20 years ago, and that I still utilize with various heelflip variations whenever I can't get the flip right.
Tap the toeside rail of your board by extending your ankle straight downwards (like how people do late flips), to help flip the board. It's possible to heelflip this way without kicking or flicking whatsoever.
I'd still combine it with a diagonal kick off the nose, but while you're still figuring out the trick, this little downwards tap can really help. It allows you to keep the board right under you, as you don't need that exaggerated flick that will often throw the board forward or behind you.
I use this to get a better flip for double heels, inward heels, nollie inward heels, halfcab heels, etc.