After car is running the oil gets dispersed throughout the engine. When cold it drains down more into the pan (although some does stay in various parts of the engine). Depending on the car, the level may change only slightly. In the TT cars there's a quantity of oil in many places other than the pan, (ie turbos and oil cooling system), which may be why the level changes less so than on other cars. To the best of my knowledge all car mfgrs indicate level should be checked warm.