Unless there is a structural bias in the traded instrument slippage should have a basic symmetry on entry and exits.
Slippage ratios of 5:1 to 8:1 between entries and exits is not normal.
More information is needed, such as a volatility measure before entries and exits.
Asymertical slippage is a usual thing for momentum driven sclaping strategies like mine. I am entering the market when it moves and exiting when it is getting flat.