Not an instructor. Adding to the hand position thing. I recently started paying attention to how the cue feels to my ring finger. For me, it should feel as if the cue is balanced there. This stays the same when having to jack up, so seconding the checking that hand position doesn't change. It may feel weird until you figure out the stance (along with hand feel) for jacked up shots, but they really aren't terrible once you get that part figured out.
We all know that jacked up shots can cause problems, error is magnified since it's approaching masse type action. The key on jacked up shots is to stay as absolute close to vertical axis as possible along with a clean stroke. You can use english but your percentages will go down.