In referencing a 22-foot (really 20-21 foot) maiximun lake level it's important to also note that was based on older inaccurate elevation measurements — ones that were about 3 feet higher than current measurements.
In 1924, the U.S. Corps of Engineers issued its first regulatory permit for Lake Okeechobee water levels. That maximum level was 15 feet — which would equate to about 12 feet now a days.
(The natural ground elevation around the lake is 14 feet or higher except for along the southeastern edge where the subsided muck land is almost as low as 8 feet in a few places — instead the 12 feet elevation that it had been.