OP:
it depends on several variables but, on my jump cue, I use in-between a nickel and dime radius.
Using more radius make it more touchy but "I'm" much more proficient with it than with a nickel or flatter radius.
I also use a 12.7 shaft instead of the thicker shafts some "think" are necessary.
My jump shaft weighs 7.75 ounces.
My entire jump cue weighs 15.5 ounces.
My entire jump cue is 46" long....shaft is 29", forearm is 12" and butt/end is 5".
The balance point when cue is together is dead on the joint.
People "ASSUME" way to much with jump cues. They are "the same" as a playing cue. You/me/everyone can/will be more efficient if the jump cue is tailored (made) to "fit" us.