This is incorrect. The coolant level should be about an inch or so down from the top of the fill spout. This gives room for expansion. If it's too full, it'll only push it out of the radiator cap relief valve
That is true if you do not run a overflow bottle / recovery system what ever you want to call it.
(For the record I run a pressurized open system with an inch to the cap, no overflow bottle and have never dropped a drop of coolant)
The op IS running an overflow so the coolant should be 100% full and about 1/4 full in the overflow.
The overflow MUST have a vent so as the coolant heats and it's volume gets larger (ideal gas law PV=nRT) it goes into the overflow and the air above the 1/4 full overflow can be pushed out of the overflow bottle.
At temp the overflow might be 3/4 full.
Then as the coolant cools, it's volume gets smaller and pulls coolant from the overflow bottle back into the radiator.