Hi, Ok, The float position should only be read when the engine is dead cold, no started up but first thing in the morning.
Sounds to me that you do not have enough coolant in:
1, check the float level prior to starting up but only when the car has been left over night, top up as required.( slowly )
2, Its a waste of time checking the level without the car being left over night.
3, you may have air in the system, but this should self-bleed or you can undo the bleed screw on top of the expansion tank, while the car is running to let air out.
4, It may take up to 2 weeks to get the float to the correct level or 10 minutes, it took me 4 days after changing the water pump,
Good luck, any probs, get in touch.