I am only having a little trouble figuring out the best way to utilise OrderModify on an ECN broker.

Basically, I place the order:
ticket=OrderSend(Symbol(),OP_BUY,Lots,Ask,Slippage ,0,0,Test EA,16384,0,Green);

Then another line have:
OrderModify(ticket,OrderOpenPrice(),Ask-Point*StopLoss,Ask Point*TakeProfit,0,Green);

But if the market is moving fast then the takeprofit and stoploss will not be put relative to the entry position, but rather be placed on the Ask at the time it's modified.

I attempted the following:
OrderModify(ticket,OrderOpenPrice(),OrderOpenPrice ()-StageStopLoss,OrderOpenPrice() Stage*TakeProfit,0,Green);

However that throws an error in the console and also doesn't accept the change order.

Any thoughts? Thanks!