Its not so much the primary grind angle that dictates the edge bevel angle, its the overall geometry of the blade itself. A 10 degree inclusive grind on a knife that is 1/4 inch thick at the spine is not the same as the same grind on an 1/8 inch thick blade. Next is how close to zero the bevel is taken. A zero ground set of matching bevels on that 1/4 inch thick blade does not pose the same possibilities as does the zero ground bevel on the 1/8 inch thick blade. Selecting the correct edge bevel for a blade must take into consideration the job to be done for sure, but its the geometry that dictates what level of sharpness and how the edge functions during cutting. Grinding a "concave" secondary edge seems a contradiction in that the only place it would improve the cutting ability of a blade would be on a blade used as a camp tool; but in that situation its not keenness that is called for, its having a durable edge. If working on a blade where slicing ability or keenness is the goal; a change in geometry would seem a better solution than grinding the secondary bevel into a concave shape.