When you use analog input for trims, SmVim sets it's default step precision to 300 steps (the maximum is 1000). It's not so "sensitive" for trim control
But, to use analog inputs, you need good potentiometer, very good, preferable short and shielded cables, good stable 5V power for your potentiometer, else you can get constant trim fluctuations even if the sensitivity is 300 steps. Also, use the pot with 2-10 kohm maximum.
You can change it to any other, maximum to 1000 (try 200 first to test), but it can be not enough in your case, see notes below):
A3 Elevator_Trim_Position p=200
1) For trim use a multi-turn (10 turns) potentiometer. The example you can see on this photo (black cylinder on right side).
Using some standard (300-degree turn) pots is very bad for trim. It's good for other controls - engine handles and yoke axis.
2) It's better to use encoders for the trims - this is always precise control (with acceleration as option).