It would all depend on your strategy, and your trading leverage from my view.
If you use 3-1 leverage and a trend following system it makes alot more sense to scale in and allow large enough steps to cushion against any loss and still allow youself to apply that extra position size with your leverage.
If you measure your position size based off of your margin you can get really hurt by small movements, but if you measure your position size based off your equity, you are letting a huge advantage pass you by.
This is something I have thought about a fair amount and have come up with no magic formula, but if you have say a 10k account, and were trading 5 positions, 2k allocated to a position with 3-1 leverage, so 6k per position total.
I would use a simple approach of a 10% stop, scale in at 5% gain then again at 10%, moving your stop up every time you scale in.
Really simple and basic, but how else would you do it?
