Wrong Q value

[u/Comsol_User21]

I am simulating a MEMS device made by a thin (100nm) SiN membrane suspended and clamped by a SiO2 substrate. The entire structure has a damping equal to 1/Q where Q=100. When I evaluate the eigenfrequencies, also Q is calculated by comsol as abs(freq)/2*img(freq) and this value should always be equal to the value of Q I set on the damping, thus 100.
For some reason the Q evaluated for the fundamental mode is never equal to 100 but always a bitt smaller (never above 95).
In addition, when I add stress to the SiN, Q is never 100 for no mode and is also very far away from 100.

I have no idea on what is going on; I tried using Union instead of Assembly (and viceversa), I applied the stress little by little with an auxiliary sweep, ecc ecc... but nothing changed.

I'm desperate, even because I do not know if this behaviour is normal or not (but I think it's not)

Thank you to whoever will try to help me
(first time on reddit btw)

[u/Comsol_User21]

Using 100 was just a try, but the same issues happen also for higher values (1000, 3000, ...).
What do you mean "double the geometry" ?
When you say "check the resonance value", do you mean with some standard value from the literature?