the pop-up's own height, measured rather than assumed
Optionalkeypop-ups sharing a key are stacked apart; leave it unset for one that stands alone
Where the pop-up is placed, at its centre - stacking moves the older ones, never a newcomer.
This is the box the rise happens inside (FloatingText rises its own inner layer), so the
arithmetic below compares where lines are put rather than where one frame caught them: a burst
stacks the same way whatever the frame rate, where Java compares live positions.
One pop-up the stack knows about: where it sits right now, how tall it is, and what it stacks against.