When you bend more at the waist, it changes the position of your hand on the ball at the release point, and will cause you to lose some of the leverage you have on it.

 

 If you can stay a bit more upright, and use more knee bend to get the ball down onto the lane instead of bending at the waist, it will give you the opportunity to "stay with" the release and not "top" the ball as much at the release point.

 

 This is a problem I have myself, and since my knee is bad on my slide leg, I often catch myself wondering why my shots look decent, but just don't seem to be "hitting" like they should, and it ends up being this bending at the waist instead of the knee, causing me to lose leverage.

 

 There is a point that exists that will optimize the release, but, since each individuals physiology is different, that point will also be slightly different for every bowler. With some concious effort and attention, you should be able to find yours.

I agree that bending too much at the waist is a shot killer. Here is one of my theories as to why it happens so often.

 

Where do many people have their first target on the lane? The arrows.

As we go through our 4 or 5 step approach, and get closer to the foul line, our eyes want to stay focused on that target. Our head starts to drop, followed by the bending at the waist... You don't feel it happening, but others can see it gradually happen. Another clue will be that after release you will fall off to the left (in your case) because you will be off balance. It's very difficult to stay balanced when you bend at the waist too much.

 

Try to follow your target further down lane as you get closer to release. If you are fortunate enough to have newer lanes with markers down lane that helps, but you can still do it by focusing on a 1-2 board area and you will become more adept at having 2 or more targets on your intended line to the pocket. Good luck.