Correct fluid level
The transmission fluid should be checked at normal operating
temperature 180°F-200°F (82°C-93°C) on a level surface. The normal
operating temperature can be reached after approximately 20 miles
(30 km) of driving.
This is from the 2013 SHO manual for the 6F50/6F55 transmissions. So yeah, I am inclined to go no higher than that spec.