I still do not really understand your problem with the concept of drawdown percentage. Neither of your examples is related to it. DD% is a very simple calculation that is used in most trade platforms and described on many websites:

When a system makes $100 profit with $50 drawdown, its drawdown percentage is 50%. If it makes $50 profit with $50 drawdown, its drawdown percentage is 100%. If there is no profit, its drawdown percentage is infinite.

- As to the check of stratey expiration, we compare the drawdowns so far with the drawdown that is displayed when you click "Test". The algorithm is considered "expired" when the real drawdown exceeds the projected drawdown. You can easily do that yourself with a test run. Only difference is that we check the drawdowns of all Z components separately for removing possibly expired components from the portfolio.