Since it's March in Wisconsin other than checking the fit, I really can't say how it will perform during fly season. But I can say that being informed the size runs big is true. I chose small pony for my Shetland and wouldn't want it any bigger.

This fly mask fits perfectly and does the job effectively.We have had great difficulty in finding suitable items for our Caspian Horses (small pony size) .and are delighted to find a quality product.

I bought the pony size for our 13 hand Welsh and it is way too big.

I got the small pony sized fly mask for my mini donkey because it was the smallest size I could find. It’s still a little big on her but the Velcro is working great. It’s been a week and she still has it on. Even when she rolls around in the dirt it stays put. Her eyes are looking much better since she’s been wearing it. It’s great quality. Thank you!