I have also to throw in my two cents.
One should work according the safety regulations and some recommended recipes for microwave assisted digestions.
The mass range for tissues is usually 0.5 up to 1 gram for a 100 mL vessel. Using too much sample material and acid can produce a too fast pressure built-up so the safety valves and interlocks may not work ok. Especially organic material should be left for a few minutes unpressurized with the acid to let the fast oxidizing reactions pass.
Recommended max. sample weights are not to make the chemists life harder, but safer.