The rudder is yaw control on the ground and in the air and what you are experiencing is left yaw caused by all the things discussed interacting to some degree. Taildraggers, depending on the design, size, engine, prop, scale shape will experience more left turning tendancies on take-off than a comperable design, size, etc. tricycle gear airplane whether model or full size. Some designs are better at handling all the left turning tendancies and a mimum amount of rudder input is required most of the time where others (like Cub) require vigilant rudder use, but either way, it's a learned skill and no amount of mixing or preset will work precisely on every take-off run.

Another thing to remember is that the rudder doesn't become effective until a certian amount of airflow (spiral or not) is flowing over it. Again, some designs are better than others so you have to figure out what works for you. I lost count of the number of times my 80" Hangar 9 J-3 Cub when roaring off to the left and cartwheeled through the tall grass before I started to get the hang of it. Getting my private pilots licence a few years ago brought a lot of insight into my model flying and the model flying helped with learning to operate full size.

Every take-off and landing is a unique experience where you have to balance speed, power, angle of attack and energy to make it work the way you want and not just be along for the ride.

Jaybird