The anger divisor controls the number of turns the unhappiness will last (all things being equal it should be the number of turns, but other factors can influence that as well).
Constant unhappiness regardless of sacrificed population is part of the mechanic: it's meant to encourage you to whip wisely (i.e. not to finish every odd building that has 20 hammers left) and offer you an opportunity to get rid off excess unhappiness by sacrificing a large part of your population (you'd be stuck with unhappiness in the early game if unhappiness scaled with population loss).
Constant unhappiness regardless of sacrificed population is part of the mechanic: it's meant to encourage you to whip wisely (i.e. not to finish every odd building that has 20 hammers left) and offer you an opportunity to get rid off excess unhappiness by sacrificing a large part of your population (you'd be stuck with unhappiness in the early game if unhappiness scaled with population loss).