Thanks for the response all, and the PM Brad.
It was a very simple innocent question. The only reason I ask is that I found that using 2% rule I regularly hold shares with total position well above my "notional" capital (which I use to size my positions). E.g. 10 positions with average stop loss at 10% (representing 2% of capital each) would have total position size 200% of the capital, implying some margin is needed. Further, as I trail the stop up and want to open up more positions, the requirement on capital further increases.
I have been fortunate to be able to open as many positions as I like because I am not (yet) capital constrainted. Just feel slightly funny in one sense that I could be 200% cash in shares, at the same time my risk in market is only 5-10% of my capital.