Firm squeeze sounds like maybe the pistons are sticky combined with a slightly out of true rotor, plenty of guides around for cleaning pistons, if you can't find one I'll write it up later, been driving all day and am now cooking so that can wait, just don't pop one right out doing it.
What’s the bike and caliper? Sram calipers don’t have the biggest surface area and I have seen them slip on hollow carbon forks. Could possibly be helped by increasing the friction under the boot head and / or caliper depending on the setup?
Firm squeeze sounds like maybe the pistons are sticky combined with a slightly out of true rotor, plenty of guides around for cleaning pistons, if you can't find one I'll write it up later, been driving all day and am now cooking so that can wait, just don't pop one right out doing it.