This's totally against my experience. While engine oil may expand when hot, but the volume increase is very minimum comparing to some other fluid such as ATF. That's why we've seen the manufactures which always require the ATF temperature measurement while checking the ATF level as the volume would change significantly with temperature changes. But we've never seen any car manufactures which asks to check oil temperature while taking the oil level measurement. The oil level will always be a bit LOWER when engine is hot. The oil level is lower is because plenty of oil hasn't got drained back to the oil pan, and it has nothing to do with oil temperature. Making sure most oil drained back to oil pan is the key to measure the oil level, not the oil temperature. That's why I prefer to check oil level the first thing in the morning before the engine start and this's the preferred way since my first vehicle. Also with this way it's very easy to read the oil level on dipstick without the need to wipe the dipstick clean.