Expansion Tank Levels

[Bill UK]

Probably a bit paranoid about the coolant expansion tank levels, like most of us who have had their fair share of BHG`s. I haven’t found any information relating to what should be the normal increase in level after an average journey, (if there is such a thing). So lets say the thermostat, water pump, radiator, rad cap, fan etc are all working correctly, what would you expect the level to be increased by from a cold start up to the end of 40 mile trip. This obviously depends on county, climate, altitude and driving conditions. In theory water expands with temperature the nearer the boiling point the larger the increase in volume. Can anyone give me some increase in levels on their Supra?