Bill Tindall
If the grain isn't laying flat the blade must cut through wood fibers, not just wedge them apart. You all know that a low angle plane is better at slicing fibers because that is what you use for end grain planing. If the blade is sharp and the angle low there is no tear-out because the wood fibers are supported by neighbors while being sliced.

However, low angle applies more, as Kato and Kawai call it, "levering force" to lift these fibers ahead of the blade tip if these fibers angle into the direction of planing. *If* the mechanics of the plane can work to prevent this lift, tear-out will be eliminated. The function of the mouth to prevent lift is straightforward. Getting things just right for optimum "cap iron effect" as Kato and Kawai call it, is not. The mechanics of the cap iron and the mechanical properties of the wood must interact in a way the converts a (plane pushing)force perpendicular to the lifting wood fiber to a force that pushes it down. An analogy might be sailing which I don't understand other than a wind pushing one way can be made to push the boat another.

Knowing the resources that a company can and will apply to optimizing a mechanical device(Supersurfacer) I can believe that a 40 degree bed angle and 30 degree blade bevel must be optimum for dealing with a wide variety of hard and softwoods. On the other hand, if one sufficiently searches exceptions can likely be found. If the exception is some wood or wood figure that is rarely used in building stuff this discovery does not detract from the utility of the conclusion. It would seem that effort and electrons would be better devoted to exploring the utility of the cap iron effect in more relevant timbers.

What the Kato-Kawia video and papers have done for me is teach me the mechanics of how a plane blade interacts with wood fibers. Whether I ever employ this knowledge or not, the insight gained has been rewarding.