frost, before going further, I would answer the question of why your baseline percent profitable is > 50% for long and short. It may be correct, but I question it and you question it. If you get through tests of 10 indicators before figuring out there is a problem with your procedure, the results will be meaningless and you will have to start over.
A few suggestions:
If your random trades are generated as 1 lots, you might instead scale based on the previous day's volatility.
I would also look at whether it makes sense to use average and standard deviation when looking at thresholds for returns since they aren't normally distributed. Quartiles might make more sense.
Edit: On second thought, the distribution of returns in this case might actually be normally distributed. I'd have to look at the data. I think it still makes sense to look at using quartiles for your cutoffs and see how it affects your results.
A few suggestions:
If your random trades are generated as 1 lots, you might instead scale based on the previous day's volatility.
I would also look at whether it makes sense to use average and standard deviation when looking at thresholds for returns since they aren't normally distributed. Quartiles might make more sense.
Edit: On second thought, the distribution of returns in this case might actually be normally distributed. I'd have to look at the data. I think it still makes sense to look at using quartiles for your cutoffs and see how it affects your results.