How to grow a long mane?

I have a 4 year old Quarter Horse gelding who is Hancock bred (a line of which I have not known any horse to have “good” hair, lol).
He is 100% pasture boarded. Braids do not stay in well. We live in Florida so rain and humidity are awful. He gets rice bran currently for skin, coat, and fat. He will be switching to flax soon (barn management decision, I don’t mind). I only comb his mane once every two weeks or so, with tons of silicone-free detangler, to make sure it doesn’t mat up. I have tried MTG, a mane ‘conditioner’(orange product), and the Eqyss Mega-Tek.

Anyone have any other tips or ideas? I have gotten about 1-2 inches of growth in a year.

Here is a picture of his mane from earlier this year (~March/April)

Some horses just don’t grow a lot of hair. Of mine that did, I never touched the mane except to cut off a foot when it got in the way, and once a year bath with Orvis soap and detangler for mane and tail. Less is more.