The video is good and does make sense. Yesterday, I was playing around with my old Lyman GPR (side note: I highly recommend the L&R RPL flint lock upgrade). It also has a hooked buttplate and, yes, without realizing it, it does naturally settle to the upper arm when mounting cross-body offhand. I'm sure the SMR would do the same. By contrast, a T/C Hawken holds more to the shoulder pocket.
On the original question of stock drop vs. tall shooters, I can't agree with the one-size fits all point of view. Many body types do adapt remarkably well and find a way to shoot any given rifle. However, with age we also become less flexible and adaptable. With modern bolt actions, a classic straight stock is considered the ideal by many. But, if I bring a classic stocked rifle to my eye and look through the sights or scope, only the toe of the stock is actually on my shoulder. Most of the butt is above my shoulder. It's the same for my son who is 6' 6". Most people would say they can shoot any rifle fine and that's likely true, but many of us giraffes with long necks are scrunching and cramming and adjusting to adapt to the stock without realizing it. Although many hate them, I find a Monte Carlo comb, or better yet California-style stock, on a bolt action fits much better with the added drop. Stock fit is a problem for me. So, I really do appreciate those who have shared their experiences with the Kiblers. It's very helpful. Thanks!