i dont know the numbers. do it a lot. some guidelines though:
if the falco doesnt DI at very low %: usmash and follow
if falco doesn't DI at like 25-40% ish, maybe lower:
utilt -> regrab or usmash or utilt or whatever you think is most appropriate. there is probably someone who can give you % specific advice, but basically going on feel will give you a good amount of damage if you know the characters well. at some point pivot grab is best... not sure on the numbers, again.
if falco doesn't DI above that range:
charge usmash or FH uair.
If falco DIs:
you can regrab for a really long time. going for weak nair (sh early, throw the nair early, hit falco with the part of the nair close to the end of your sh) and then regrab or, at higher percents, usmash is good at some percents too. i'm not particularly good at this, so ask someone else for advice. or just watch colbol vids. colbol absolutely destroys falcos with these kinds of setups on FD. it's a beauty to watch. other players do it too, but Colbol is the most instructive imho.
edit: also, there was an M2K post I read about the percents a long time ago. i have no idea where, but digging that up might help you.