How to Maintain "Fixed" Value Position for Hedge?

My first post here. Apologies if this topic has already been covered; I searched the threads but could not find coverage.

I want to backtest a simple strategy using an equity ETF as a short hedge against a long strategy that picks stocks using PositionScore. To simplify the procedure, I will to run the hedge backtest separately from the long strategy and merge the equity files in Excel. Here is the hedge strategy:

Day 1 Short position value = $100,000 (Say SPY at Close)
Day 2 and onward: Short more, or cover part of the position in order to maintain the same $100,000 position value based on that days Close price.

I realize this is scaling in/out but can't figure out the proper AFL function or code to use.

Thanks