Fuel pump replaced...but

I just replaced a fuel pump for a 91 Eddie Bauer Explorer 4x4.Everything went as planned but I noticed the replacement pump had a different float.The old pump had a round float and the new pump was identical except for the float was more of a flat type float.After I filled the tank with 19 gallons of gas the gauge only shows 1/2 tank.Anyone know why this is?This pump is suppose to be a replacement for the pump I had.everything fit exactly.Anyone have an answer or had the same problem?