I think it's not just fighters. Anything with a short deployment time gets reduced crew. That's one of the reasons that commercial ships have to have at least 3 month deployment clocks.
I missed the deployment time varriable versus the crew amount drop.
Tought first time it had something to do with "Crew Quarters - Fighter" item.
When i dropped down the size of 500ton, it sayed:
"This design is classed as a
Fighter for production, combat and maintenance purposes"
When i add a Very Large Fuel tank, it says:
This design is classed as a Military Vessel for maintenance purposes
I think in the calculation should be;
IF deployment time is Lower then X,
AND Unit is less then 500ton, then drop Crew amount, based on the current calculations.