I'm trying to calculate my return on investment (ROI) for an options position on margin that has been rolled. I'll give an example:

1. Sell to Open (STO) a naked put position, for which I collect 100 premium, and the margin put up is 1000, for example. I have 1 contract.
2. Roll the position by Buying to Close (BTC) the short, which costs me 50, and then STO another naked put for 150, with a new margin requirement of 1750.

I know each transactional ROI:

1. STO 100/1000 = 10%
2. BTC 50/1000 = -5%
3. STO 150/1750 = 8.6%

My question is, what is the overall positional ROI, calculated from these transactional ROIs? How to weight each ROI?

Is it weighted according to the latest margin, so:

10.1000/1750 - 5.1000/1750 + 8.6.1750/1750 = 11.45%?