Minimum 8" down from the collar.
No one walks around with their hood up all day,
and if they do, don't worry about it from a printing perspective ( or life, and 8" is still low enough for both )
Zip hoodies, you gotta go lower, the hood will hang lower because of the split front.
Zip hoodies are usually worn open, so the hood hangs lower.
But, it all depends on the brand, so, have a look at how it is.
( end of 'safe' advice )
Both styles of hoods vary greatly in how they sit on a bunch of different shoulders.
Basically, you're totally f*cked no matter what you do.
Someone will bitch.
Loudly.
and you're the assh*le no matter what you've tried.
Embrace that.
You will become a screenprinter of hooded fleese garments.
( hey Doug, do I sound like myself yet?, lol )