I have a 2013 MKZ Hybrid - same fuel capacity of 13.5 gal. On my fillups, I just go to where the pump clicks off, no top off's. I like the consistency to manually calculate my MPG. I've never put in more than 11.55 gal and it is usually in the 10.75-11.5 gallon area. I tend to fill up when the DTE is as low as it will go on the dash. The 10.75-11.5 fill shows as Full on the dash.Just purchased 2016 mkz hybrid,previously owned a 2012 mkz hybrid, never had issues filing that tank,but this tank seems very sensitive to reach the full mark. I know capacity states 13.5 gallons,but at one fillup I reached 13.5 gallons and tank still wasn't completely full.Any thoughts on this?
Don't know if this helps or even answers your question, but it is my experience.
The owners manual states to allow no more than 2 click offs when filling.