After Karissa and Laura pointed out to me that Belle was hitting three times on the down ramp from a stationary start on the DW and twice when we began with a running start, I watched several of my previous videos paying particular attention to Belle's striding. I contacted Silvia Trkman and she watched the last video I posted. She wasn't concerned about the three hits from a stationary start on the DW, but, as Karissa and Laura observed, she told me that Belle needs to extend her stride a bit more when running so that she can hit lower in the contact zone.
We are to the point now that a large number of reps per session isn't really necessary. Instead I'm hoping to do 6-8 reps and concentrate on either getting Belle to extend her stride or introducing turns after the DW. I also want to introduce having a tunnel be the next obstacle, but first Belle will have to become accustomed to running because I'm running and not because there is a target ball waiting for her. I lowered the DW to three feet for now so I can introduce the turns, and I'll probably keep it there for another week or two.
I really like this method of teaching running contacts. When I attempted re-training just the A-frame using Rachel Sanders method 16 months ago, I had Belle doing way too many reps in a week and she paid the price. Knock on wood, this seems to be a much less physically stressful way of training running contacts. The only problem is that not everyone wants a running DW and for Silvia the running AF is just a natural consequence of teaching a dog to do a running DW with her method. Of course, you could still use her method and once you have the running AF you want, then you could teach your dog a 2o2o DW.