Thank you, that's very kind of you to say so 
I dont have any Foundry figures but my understanding is that there are at least 2 sculpting teams for Perry Celts.
The Perry brothers have done the earliest range which are quite small and probably the figures people relate to as 25mm.
Rob Baker has sculpted a range which are I believe larger and would fall into the 28mm bracket.
I'm not sure but I think Mark Copplestone may have produced some figures for Foundry which if true would also fall into the 28mm bracket
Copplestone produced four of the Gallic Cavalry sets and one infantry set, the rest of the Gallic range was done by Baker. These are all large 28mm that fit with larger figures like Victrix and Crusader. They are listed under the Gauls range. I don't have any of their chariots but the cavalry horses are huge like Victrix and Crusader's horses.
The Perrys are mostly smaller but some are chunky enough to use as shorter warriors alongside bigger 28mm, their chariots and cavalry are too small to use beside larger 28s. They appear as Ancient British Celts or similar on the site.
The third group are done by Dave Gallagher and appear as Continental Celts. They are mid way in size between the other two but match the Perry Celts more in size and style, especially their horses and they use the same chariot as the Perry Celts.