Observation:
You're kinda setting yourself up for a problem anyway. You're trying those forearms on bare armed. Your shirt is going to add size. And it looks like the wrist is so skin-tight you'll never get your glove cuffs tucked up under the armored wrist anyway-Though that's a guess from just a couple pictures so I could be wrong.
Plan A - TwoPart the wrist. That way your hand goes in since there's a big slot. Then the second part goes on giving you a good seal at the wrist.
View attachment 363621
Plan B - Increase the size of the wrist in less simplistic approach than increasing the entire part.
IE: Flare the wrist like the big end of a funnel, by 5% or whatever rather than make all of it bigger.
You could do that in blender... in Armorsmith... In MeshMixer...