When the temp control dial is on hot, there is hot water flowing through the heater core whether the fan is spinning or not... so some heat is definitely going to drift off of it.

Engine efficiency has nothing to do with it... all modern motors warm up to approximately the same 180-200 degree mark. Maybe the X is missing some extra baffling or insulation that might keep you from feeling the radiated heat in another vehicle - but any vehicle will heat up just the same.