Half bubble can mean very different things on different levels; the bubble to angle ratio is in no way standardized (at least so far as I know).
Check the manual for the fridge, but I think Dometic usually just says "so that it's comfortably level in the RV" or something similar and equally nebulous, while Norcold specifies somewhere around 3 degrees max out of level. Three degrees is really quite a little bit; it's somewhere around a five inch difference side to side for most RVs (i.e. those around eight feet wide).
If you're trying to gauge the fridge temperature based on what the air feels like to your hand, that's not a particularly reliable measure. Better is to put a dish of water in and let it reach equilibrium and then measure the water temperature with a thermometer. (If you can't put the thermometer into the dish of water, the fridge is running a little too cold :B )