IB Slippage


I have an average slippage of at least 0.5% between C2 and my IB account on Market at open orders. Is it normal? Does someone have the same problem? Do you know how the get better fills? Perhaps change broker? My last huge slippage:

27/5 APP Sell at open C2 fills 1.68, I fill 1.61

Please help with this.