Due to the primitive state of explosives technology in the early-modern (c. 14th-18th centuries) period, grenadiers were usually soldiers selected for their size and strength. It was important for them to be strong enough to throw grenades with enough force that they didn't fall short and land near friendlies.
Therefore, I suggest to make strength increase the range of thrown grenades. It makes no sense for my tiny undead female mage to be able to throw a grenade as far as a big beefy Orc.