I'm presently going thru bar knocking problems with Fei. I guess I'll have to make sure that I train at 24". Everybody tells me it's a baby dog thing but I've never had one knock bars like her. Of course I've never had one quite as fast. It seems like it's always something.
I think part of it can be the fact that they are not as experienced, but there are so many different things that affected dogs jumping. Knocked bars can have so many different origins, it can be a puzzle in and of itself to figure out the source/cause of the bars.
Fei sounds a bit like Draco. He is extremely fast and driven with an incredible stride length. He tries hard to clear the bars, but knocks bars periodically. It only takes a split second decision on his part in regards to where to take off, and which direction he is turning. If he misjudges the takeoff it can mean he skims the bar and knocks it. He REALLY flattens out in straight stretches and off the start line, increasing his potential to knock bars.
Draco just needs a lot of experience in judging the different situations. In these cases I work a lot of jump grids with varied spacings and heights. He has to really think about here he is taking off and how high he has to jump.
Ava on the other hand has something different. Ava is and always will be a bar knocker. She has what is called "Early Take-off Syndrome" No matter what we have done to correct, fix or alter her jumping she can not correctly determine the correct point to take off from. She jumps WAY early, so the arc of her jump is on the downward slope before she even clears the bar. Of course when she knocks a bar, it only further intensifies the problem. Because of her poor jumping she can only run on certain, more forgiving, surfaces. Ava is handled very carefully to reduce the pressure on her to take of her, placement of crosses to alter her take off point are helpful.