My experience is that propane camping stoves have very lopsided flame adjustment. The knob may rotate two or more turns, but the first 1/8 turn goes from off to 95+%, and whatever difference the remaining rotation makes is pretty much undetectable. Why is this?
The propane flow is dependent on the pressure in the cylinder, and depends strongly on temperature. See the vapor pressure chart of propane here. You can see that at room temperature, the vapor pressure is about 10 bar, while at 0 C it’s 4 bar, and at -20 C it’s down to 1.5 bar. The flame control needs enough range to operate under colder conditions.
If you’re looking for technical hows-comes somebody else may know. If you’re looking for what-kin-I-do-about – I assume your experience is with the common low-end green Coleman camping stove? There are camp stoves available that do have useful flame controls for simmering and controlled cooking.
Here’s a site which compares features: Outdoor Gear Lab