Do you want the mane to lay on the same side all the time or for shows? Because, as hard as it sometimes is to even think it, the hair thing is sometimes genetic. (As an appy lover, I can sooooo vouch for that one.) If there's a cowlick in that area of the mane, you may be stuck with having it split. The good news is that you can band/braid/lattice it for shows, depending on what you do. (I know, I just created a verb out of a noun. Bad girl!)
I hope you have fun with your horse, and good luck with that mane!
Learning never stops