I'm with FLOI on this one. I believe the ball swerving behind the back contributes to another dimension of lag and load.
I've mentioned in another thread that my hand and ball Naturally get in-line with my rear shoulder and head while doing the reverse-chaining drills and so does my DD's. In fact, the ball has always went behind my DD's head on the downswing so I'm starting to second guess that it should always stay visible to the catcher myself. Last night I noticed while my DD was performing the reverse-chaining drills with the ball in front of her shoulder towards 3rd base that she was throwing the ball way outside (RH hitter). It seemed the ball path was going from more outside her body slicing towards her front hip if that makes sense. This put the ball too far away from her rear hip in my opinion. It could be that she just wasn't coming straight down with her elbow but I'm not sure. It does seem that if the ball is right in-line with the rear shoulder at 9 then the ball/hand is able to be a lot closer to the hip/thigh at release.
In a full pitch, however... I am aware that many pitchers have a moment or phase where the ball is not visible... but I think that has more to do with the rotational necessity involved in a full pitch... and the fact that the EXTREMITY will lag behind the PROXIMAL structures, because that's just the 'nature' of things. To me, this is a result... not a 'trained move'.
When I drill, I have pitchers maintain the 'ball seeing the target' concept. I make sure that shoulder/hip line isn't closing too much, that the elbow isn't oriented incorrectly, and that the ball can see the target.