Kyro, I'm 5'2" and have kind of a big butt. I usually try to ride in a 16.5" or 17" for a jumping or A/P so that the flap isn't overwhelming, but for dressage, I have to have a short flap no matter what. I used a youth saddle for a while (16", my poor butt, so miserable), and now have a Custom Saddlery that is a 17.5" but has a very short flap (custom order) so it actually fits every where. There are some makers that offer a short flap as a stock option, you'll just have to keep an eye out. It is so much more comfortable to be in the correct seat size and have the right flap.
Tug on anything at all and you'll find it connected to everything else in the universe.~John Muir