[I was on a long vacation and so the delay response]
Backtesting in Stockalyze is about testing stocks individually and not about portfolio as a whole and so it always assumes you are investing entire amount into single stock and then it gives you result about how good or bad the trading results would have been.
With this setup I don't think position size or position value is required.
Please let me know if I have explained it. In case there is something that I am missing then please let me know.