That is right. That is why I say, write down ALLLLL ways you want to exit with multiple contracts. Take a week to decide the ways.I get what you're saying. Scaling trades is an added complexity, but I wouldn't rule it out on that basis alone.
Complex things become simply with training and understanding.
If I add to a winning trade - I always have a target of where I ultimately want to exit. So on the few occassions I've done it so far, it's been pretty easy I'll say.
Then everyday just start tracking or go back test.
This is what I am doing with my own exiting methods. I have 6 ideas to exit a position. Well, I am testing them all. One exit method is exit at 3RR, well guess what. That method have big drawdown and can get about 5 losses in a roll. I personally do not like that, but still tracking data to see how it do over about 200 trades. I am tracking 2RR, it does pretty good. And I track price action trailing exit methods too.
NOW, I have an idea of what "I" like AND AND that can make me money. But it all started with writing down and researching different exit strategies first. You can ask members on the ET in a different thread to help you too.