yes, or instead of a ball, you could simply cut a few threads, and use screws with kind of hemispherical heads
if you use a ball instead of a cilinder, then you will increase grip
if you tilt the cilinder 90*, then you will increase grip even more / kindly
ps : one more thing : placing the point in the upper half or lower half, actually is taken into consideration toghether with stock slope, and relative position between vice master screw and mobile jaw; the greater the distance, among z axis, between the contact point and the screw, the bigger the stress that will appear inside the vice, and the bigger the chance for a fly off during heavy cutting; take all these with a bit of salt, since if you try to clamp 30x40 inside a small vice and machine with a o30tool, you will have less worries compared to a part that is 300x70 inside a big vice, machined with a o150tool