Working with Slippage

I try to optimize the closing trade function by forcing to close our trades with our price. What I do is checking the last known market price before sending to closing trade function. So the EA will always compare our last known price with current market price.
If the EA wants to close Long position than it must be happen if current price is higher or equal with the last known market price and vice versa. The expert will force to complete this action before new bar is coming. Once new bar is coming then the EA will wait an others logic for closing trade.
It might to be a compromise decision, because we have to decide to allow EA working with its logic at any price (no matter slippage), or forcing EA to close with exact price while allowing another logic to be waiting (back test will be differ after live trade).