I don't find it easy. I've made a lot of progress over the last week after much stagnation, but commanding just the muscles above the adam's apple is not nearly as easy for me as you suggest. Neither does holding the adam's apple as high as possible actually seem to correlate directly with a female sound (and this is while I think I've eliminated the muscles between trachea and chest), but instead my most female sound so far has actually happened when my adam's apple was about a centimetre below it's apex (but nonetheless way above where it is in normal male mode). I also have trouble squeezing the trachea laterally with my muscles, which I believe is also an important step, to reduce the size of the piriform sinuses. What I'm doing at the moment is glides down from C5 as the sound I make up there seems most female. My muscles just seem to arrange themselves properly up there with a little conscious attention to the height of the adam's apple.