Mercury says as empty as possible with ethanol fuel and you treat what is left. Full if non-ethanol.
I looked this up again so I could post a link to what Merc had on their website back maybe 5 years ago. I couldn't find it. What they post today is a little bit different.
Before: Run the tank as low as possible and stabilize what's left. Fill in Spring. If that's not possible, second choice, fill the tank and stabilize the gas. They didn't specify "how" full, just fillerup.
Now: Most fuel systems NOW are 4-stroke and are non-vented. Stabilize the gas and it doesn't matter how full because moisture can't get in anyway.
As I said before, my old woodie is kept in a dry garage. The portable tank is aft of the back seat. Due to weather and health problems she didn't go out last Summer, though I filled the tank in anticipation. So, the gas this year was a combination of 1-2 year old fills (stabilized of course). This month she fired right up and ran like a champ.