when i send a brahmin to a settlement with no settlers the settlement happiness raises 2% (so 50% to 52% for one)

but when i send a brahmin to a settlement with one settler it doesnt rise at all?

bonus happiness seems to be amount/# of settlers so should still give 2% and should still giv 1% if theres 2 settlers which it is also not giving

also for example my taffingtons boathouse has 0 settlers and 2x brahmins and its happiness is 54%

my starlight drive in also has 0 settlers and when it had 1 brahmin there was on 52%, but when i sent another brahmin there it dropped to 49%? and it also has a red down arrow next to happiness so is still dropping??