For hi-hat most of the time my heel is up, but to "sizzle" them I'll bring my heel down. I find it gives me more control than trying to do that heel up.
For bass drum, most of the time it's heel up / bury, but sometimes I play heel down or heel up / unbury using Matt's technique or by playing further back on the footboard.
It's still all a work in progress for me; I still get a fair few problems with all of the techniques I know, I've always had issues with bass drum playing, but I work on it all the time to try and fix the problems. I think that's the only way in the end.