Best I ever got out of a tank (701 miles) was 58.70 mpg (displayed mpg was pretty close at 60.1). Leisurely trip, lots of secondary roads, never exceeded 65 mph. Summertime. Briefly tried a few hypermile techniques on that trip, coasting up short steep hills and drafting, but only a few miles, not enough to affect total mpg over 700 miles.
If you have the patience (and space) to keep it to 50 mph, you will exceed 60 mpg fairly easily in good conditions. Or try a trip on something like the Blue Ridge or Natchez Trace Parkways with low speed limits.
2018 Kia LX HEV Metal Stream with Advanced Tech