Savvy Feeder - Narrow or Custom Grate

It might be niche but looking for opinions on which grate size to switch my mare too.

The original opening grate is apparently too easy for her now and she’s inhaling hay. It was not a problem last year when we were trying to put weight on her, but this year I’m looking for that sweet spot of losing her grass/hay/coming-out-of-stall-rest belly while keeping some sort of roughage in front of her (my trainer says she looks like she’s ready to foal, that’s a slight exaggeration…slight)

The company said the narrow grate could work for the grass hay and smart mare combo I’m working with or they can custom make a smaller hole if I want, but the question is how small is the right size? Thoughts?

I have the original and smaller size. Even with the smaller one my mare inhales hay.