Katherine, the dorsal sepal is the topmost, center petal, and its opposite on the bottom is called the ventral sepal. Whether the dorsal "flattens out" is a matter of genetics - and with multi-generation hybrids, it's very difficult to predict. The AOS likes the dorsal to be large, round, symmetrical, and flat, among other things. Paph. charlesworthii has been used in hybridizing to achieve just that, although a number of the Barbatum Alliance also have large dorsals. Yours just really reminded me of the shape charlesworthii has, which is why I'm surprised there is apparently none in its parentage.