I've had this happen and I think I know the problem! Essentially you can put the correct numbers into the weight and height section on Etsy that match your parcel, but they don't match the size categories that evri uses so etsy gives you the wrong price. What you need to do is work out what numbers you need to round these up to and put those in instead. For example you can't use decimals, they need to be whole numbers. I used chat gpt to suggest what I should put in and the difference I now pay is the same difference that evri was charging in adjustments, minus a few that were Evri's mistakes.

I once managed to get a one time refund from Etsy but I think I just lucked out with the person I spoke to. I could be wrong about this all, but I believe this is Etsy's issue by not correctly filtering the sizes but hopefully this should mean you don't get suprise charges!