Just in relation to the A321 having the fwd section blocked , this does happen on quiet flights due to the aircraft being nose heavy ..... Heavier at the front , normally on London flights load planning compensate for this by arranging freight and baggage to be loaded aft , however sometimes due to lack of baggage / freight this isn't possible . EI used to load ballast to compensate for this however this was considered expensive so blocking rows became the cheaper option . Also the problem with trim should only be relevant for take off and PAX should be allowed back to their seats 15 mins after take off