Shower drain re-venting question

I recently relocated a shower in my master bath and now I need to tie the 2" drain into the 1 1/2" vent again. The vent stack is only 3 feet away but I can't go up above the subfloor anymore). So I only have 5 inches of space above the drain line to work with. Is 5 inches enough of a drop for a vent before I add a 90 and run it over to the original stack?

Thanks,
James

A vent line needs to be sloped so it doesn't fill up with water and close off the venting. Both drains and vent lines should have 1/4"/ft slope. Not sure I understand your full question or planned result. Maybe a picture or a diagram would help.

Thanks, I understand the slope. The issue is, that normally the vent would go straight up off the drain pipe (either straight to the roof or take a 90 degree turn over to a vent stack that does go to the roof, and I'm looking for the minimum height the vent should come up off the drain pipe before that 90 degree turn....

I'm trying to keep the vent pipe within the joist, so I can only come up about 5 inches before the 90 degree turn over to the vent stack. Is that acceptable?

The trap arm can be 60" long before the vent.
It's best to revent at 42" above the floor.

If the vent is being washed by a fixture lave a lav, then it can be lower then that for a while.