I still think it is too low. You don't have any "smile lines", I posted a photo of P, I am collecting Photos of Bridles for my next segment of "Harnessing Up" and I found one that shows his "smile lines", I was always told that with a snaffle bit you should have some smile lines.
In P's photo you can't see them very well so I drew them in. Copy of DSC01665.jpg
In this photo of a horse I was trying out you can deffinatly see the smile lines, more than I would have. I even asked the owner if she thought the bridle was too tight, she said no. But it was tighter than I would have, personal preferance. LUCKY 011.jpg
Another thing that your mini might be having a problem with is ...didn't your harness come with a horse size bit? If you are using that bit, not only will it be too wide but the mouthpiece will be too big around, possibly preventing your horse from closing his mouth with out pressure on the bars of his mouth.