You mention that you are overweight. It could be that because when you pushed the ball out straight in front of you, you might not be getting the ball in the right part of your hand at the backswing (I haven't seen you bowl, so this is just a guess).
Typically when one pushes the ball to the left (for a right-hander), the arm will swing to the outside of the body (easily clearing a slightly larger girth), which enables a freer swing and creates a ball placement on the palm that is ideal for leverage at the release point, since usually the arm will self-adjust and the release is near/close to the ankle if timing is pretty good, then the thumb will clear right prior to the ball passing the ankle, which causes the weight of the ball to shift naturally to the fingers, which will cause a leveraged release and the necessary heavy roll imparted by the fingers without any undue unnatural force.
I mention the above after having watched many a good heavy bowler's execution.
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Regards,
BowlingWolf