So if I understand this correctly, if I have an EA which builds in 3 points of slippage, and I set Strategy Tester to a 2 (point?) spread, this means that the effective cost of the trade is:
.3 pip to open
.2 pip spread
.3 pip to close
which totals only .8 of a pip?
There is no slippage with the Strategy Tester.
And anyway you reasoning is wrong. Slippage is not something fixed.