Is it okay to run the fuel return to the top of the fuel tank or should a line be run to the bottom? I'm not sure why but it doesn't feel right to spray the fuel into the tank like you would get excess vapor or something.

Jaz Pro Stock fuel cells come with fittings in the top for return line and vent hose. That's what I run and it works great.

I like to feed it into the bottom to avoid making vapors and static electricity