Probably this is not a newsflash to most people, but that size- finder thing is just a pretense, according to how it works for me.
If I put in my “ stats”, then pick a brand and some size ( e.g., XS- L ) , it just regurgitates the letter size. No matter what brand or size I put in , it does that. ‘ cause I checked.
Maybe it does differently when you input letter size for an item that comes in numbered sizes, or vice versa, so could be intended more for size conversations.
Anyway, so far I’ve found it pretty useless, if not just misleading.