Come on Brian, most, half, one quarter, whatever, it really doesn't matter! The point is we're talking about bunker styles here and there are all kinds! I'm not advocating one style over another and you shouldn't either! The variety makes golf courses interesting, and one style most definitely should not be assumed to fit all!
I happen to love the grassed down to the floor surrounds and the "shadowy" look of bunkers because of that! I believe it actually makes a golfer pay more attention, probably concentrate better and search out a course's strategies!
But on the other hand, I can't deny and would not advocate the removal of the style of bunkering that uses the flashed up sand faces to create an entirely different look, effect and thought process in the mind of a golfer! The flashed up style certainly isn't some new and untried wrinkle as a bunker feature and bunker style and as for the ball plugging in the flashed up face, well, that just is not supposed to happen--the ball is supposed to filter down the face to a more level lie. At least that's what Donald Ross and many of the others said who used all kinds of bunker styles throughout their careers including both the grassed to the floor style and the sand flashed face style!