I think the outer perimeter of the "Relation: Lake Mead full-water area (8527067)" needs adjusting to better match real world data. I dont know where the data could be found but I do think this is useful data. 
https://www.nps.gov/lake/learn/nature/storage-capacity-of-lake-mead.htm
This page has some info on levels.
Full Pool Operational Capacity 1,219.0 ft. In the 80's and 90's it did crest above 1200 ft.