His idea of 'very deep' and the current version, are very different! Nicole and Isabel rode their horses not that much lower than that pic of Anja, more curled back, yes, but still nothing like as extreme as certain current champions! I watched both of them working in horses at the WEG, Aachen and other international shows and never saw anything that approached what would be now thought of as rollkur. The neck was extended out, lowered and then face btv, but never with the neck shortened and cramped back to the point that the eyes literally bulge out of the head, as is seen today.
The effect never looked in any way forced. I personally dont agree with it, but would have more so when that article was written. It must be 5 or 6 years old, and a lot can change in thinking, in that time! I wouldnt now ride a horse as long and low, even as I did with Rei when I first had him here 4 years ago.
You will see the young chestnut horse coming btv, in that first video of Kalman's, but it is a very different 'deep' to rollkur. I am certain that this is what Hans Heinrich meant as his perception of 'deep'.
Hope that helps!
PS it was first used to stop Rembrandt spooking, but then Dr Schulten Baumer who trained Isabel at the time, thought it loosened the back, and developed it into a training method. Reiner Klimke hotly disagreed with it and predicted it would be taken to extremes, as indeed, it was!