RE: Programming Futaba 6EX for an Axe 400
No, it shouldn't need adjusting that frequently unless there are wide temperature swings as that affects the gyro. Try to get it adjusted so there is little or no drift when switching between HH and regular mode.
The 6EX does not have a sub-trim function, only trim and trim steps. Actually this is better as sub-trim can create problems with HH gyros.