Indirect hits.
Throwing to the side of an NPC, while keeping them in the blast radius, does less damage, hence, more rep. However, this indirect assault also takes longer, uses more grenades, and costs more gold in replenishing grenades.
An effective way that "I" have used to level grenades was to go to Tormenta, use hex on two-three Molusks to bring them all within the blast radius of one grenade, then switch to grenades. I used smoke grenades (while they lasted) and used indirect throws to take down two-three molusks at a time. Once the smoke grenades were gone, I switched to using stink pot (just stay out of your own blast radius).
Yes, it does splite the points between pistol and grenades, but the majority of damage comes from the grenades, therefore the majority of damage points goes towards the grenades.
Once I am out of smoke and stink pot, I stop using hex on pistol and go directly to using fire grenades. Once they are gone, I use regular grenades.
It worked for me. That'll be five gold, thank you.