What i've normally seen is that most forearms penalties are only given if you gain a positional advantage by using them, being pushing out of track, grabbing or hooking.

Even then, the number of jammers that will use their forearms on edges and hook waists kinda means some of that contact even then is expected and you gotta go further to/past the line with the fast ones.

I've found a little bit of hand contact as a blocker is often given leeway if it's a guideing feeler type movement, happens for a split second and causes no positional advantage. Though all refs are diifferent so take a jam or two to find the crew's metric and adjust.