Have a look.... there's a ton of previous threads discussing fuel levels... Many say 1/4 tank, many say full tank... The little magnifying glass top right of the window is a search function. Click on it and type in some key words.... Happy reading/
I've done the 1/4 tank, the 1/2 tank, the 3/4 and full. Each time with some quality stabilizer. Never noticed a difference after 6 months of hibernation.