If you aren't tapping at all, it really wouldn't matter how late you come into the bar, you'll still most likely land on it. If you think about pushing your feet under the low bar then tapping (I'm not sure if this is giving you the visual of how late the tap should be or not but it seems to help my girls), you should get enough speed in the swing to come in later.
Try think of it as a really weird back hip circle undershoot. I see too many people trying to do it as a pull over, stop, undershoot and smash into the bar. If you have a good clear hip and your hand rotation is good, focusing on the undershoot instead of coming back to the bar sometimes helps.
Going back to Bob's post, when you cast, push your shoulders to your ears and hit a tight hollow shape. This in itself generates quite a bit more speed around the bar instead of just falling away. You need a circular motion like a giant to get around. If you just fall away, gravity pulls you straight down so the tendency is to swing to a stop then fall on the bar. Watch the way the bar bends with someone does giants. It makes a bit of a oval shape from the angles their bodies are pushing on the bar. The dropping into a pull over is more a straight up and down motion not allowing for the swing to clear the bar with enough velocity to do the undershoot.
I guess what it all comes down to is this:
1. Cast while pushing to a tight hollow shape. (Push hard ,you'll swing faster)
2. Look for the low bar and stay hollow until your feet pass it. (It used to be written as a deduction if you arched early. I'm not sure if it's still in there or not)
3. Push your armpits toward the ground to allow your body to hit a tightly arched shape. (Most people try to arch from the feet up. This makes for an incorrect tap timing)
4. Tap as if you want to kick the ceiling above the bar. i.e. all the way over as if you were doing a giant.
5. Eventually you should be able to feel when the bar is bending with you and when you should close in OVER the bar instead of onto the bar. Padding the bar isn't a bad idea if you don't have a spotter.