The first of these will return only non-stops between LHR and CPT, so specifying CX and EK will do nothing. The second will return connecting itineraries. However, you will still get nothing back on CX with this because as far as I can see it's a minimum two-stop itinerary on CX, so you would also have to change the "Extra stops" selection to allow 2 extra stops (or more) - plus because CX is such an outlier compared to BA and EK, you actually probably won't get any CX results unless you specify it as the only airline of these three (ie just CX+).