When you throw one of those shots that doeant appear to finish, look at it and see if there are oil rings all the way around it? if so, could be carry down.
if not complete oil rings ar very little shows on the cover, its a different issue.
Most likely the cause is that it is reading early and using up all its energy by the time it gets downlane, that looks similar to carry down.
trick is to move in towards the center of the lane a little at a time until you find some head oil