I think each horse and their genetic make up varies from horse to horse.
When Thera was born she was all legs! I was sure she'd go over come darn close. She is 5 now and is almost 33".
Then there's Treasure. Sire is 29, dam is 31.5 and she coming 3 this year is 37 1/2 :new_shocked: . Then Halley, nice small parents and she is coming 2 this year and is at 33.5". If she keeps growing I could care she's R too. Missy is 28" at 9 mos, her sire is 29 3/4 and her dam is Thera.
I'd say the filly will grow some more. If the seller is willing to give a"height" guarantee, try it. I got Halley "without" one and am very happy, I got Glow with one and the same holds. You just have to decide what you want and how far you're willing to go.
Alot depends on the bloodlines also. Treasure is lots of GMB and favors her GGdad alot!