Well, first off, the more surface area stabilizing an arrow the quicker it'll stabilize. It's a balancing act. Arrow weight, FOC, form etc all fall into the mix. You'd never beable to convince one of these X shooting world class archerrs you can't shoot small vanes as well. Most shoot tiny vanes. They're the best and could shoot a broom handle if they could get it balanced. I think it's probably a combination of things for you. Probably some form, maybe some bow tune and the physical difference of a smaller control surface. A fixed broadhead should really magnify any of these concerns. It may be set up, you, arrow ... It may just be they aren't for you. If your groups have opened up with them, I'd change something.