I think that "suspended" is somewhat analogous to "floating." You can, however, suspend an object that is heavier than water in the tank by hanging it from a wire... thus making the terminology open to interpretation.
If they’re looking for mass/body fat/etc, then the interpretation of floating would be more likely.
Since that was the intent of the procedure, as opposed to someone having a nice swim, the people doing the procedure would know that immersion was not desirable.
I’ve talked to several people, at least two in bariatric settings that carry out one procedure, while I’ve talked to military recruiters about being “dropped in the tank” to measure body fat % and they describe something different; but in both cases, they said nothing about a person’s head going under water.
Point is, there’s more than one set procedure, just as there are differing applications.