One thing to know about the 9 ball rack is when its hit by the CB the entire rack shifts back while still together something like a 1/2" or something (this is the reason why the wing balls can cross bank in to the corners)
Thefonz's comment about basically not cueing TOO LOW is true, first off the lower you cue the harder it is to hit the horizontal center accurately with no side spin (english)
You don't want to Draw the CB off the 9 ball rack anyways, you want it to hit square and then stop pretty much in the center table area. So at most the "draw" which usually is just the CB springing a tad back after contact and just dying there maybe a diamond length.
So either a very slight inclination can be used with a center CB hit for a pop back, or level cue with a SLIGHT quantity of low.
Whats happening most likely could very well be actually that you are hitting the 1 ball just a smidge off square to the LEFT of a FULL SQUARE HIT
From the angle you set up the break, the very slightly off full hit, too much backspin/draw.......and the fact that the rack is going to shift forward would change the carom angles start of the CB off the 1 an extra 1/2" +/- closer to the foot rail. The over application of draw pulls the CB back toward the opposite side pocket and a possible scratch.
If there were no draw on the shot the CB would have just been directed pretty straight to the side cushion from the head of the rack.
If the rack didn't shift back upon impact your same break shot using low draw would drive the CB into the long rail on the head end of the table past the side pocket.
A perfect break in 9 ball is pretty much just a stop shot, as the velocity is enough that the CB is SLIDING into contact, not rolling.
-Grey Ghost-