Hi,
The simplest and most robust way to calculate if anything is going to hit you or miss is to see:
1) How close is it?
2) Is it getting closer?
3) Is the relative bearing constant or changing rapidly?
4) Will it hurt?
If the answer is getting closer & constant relative bearing & relative height < X ft then the answer is yes it may hurt therefore warn.
If the answer is closer but bearing changing rapidly or relative height > X ft - then just advise.
If the relative height is 1,000 ft or more (+/ a bit for error) then don't say anything.