I actually have a similar horse who is very shy with the bit. The moment I put too much pressure on the reins, my horse goes tense and refuses to move. I'm not yanking him or anything, he just is afraid that he will get hurt, so he 'paces' himself for what is about to come. The reason for this is his last owner, who treated him horribly.
What worked for my horse, is really light-contact with the reins and similar light leg aids. A lot of transitions! For example: 6 steps walk, 9 steps trot, 6 steps walk, etc. Also, to get her to go softer on the bit, you could try doing a lot of figure eights, circles, extensions, collections, stops - so she will always be listening to you. This also makes her want to balance herself better and bend throughout her body, therefor making her more elastic and relaxed.
Also, I don't think your heels aren't down enough :) there are some pictures where your toes are facing outwards, though it's hard to tell. Like somebody else said, you don't want that, as you start to use the wrong part of your leg (and it's not pretty when you go to a competition, even though a lot of riders ride like this, not knowing there's something wrong).
I always want my foot to be parallel with the ground, like when standing. But if the heel is down too much, it could cause your leg to cramp (not a nice feeling ._.).
I'm not a professional, this is just what I'd do and my opinion :)