I don't think the grenade does that. Since the big robot has a much larger hitbox, all 6 spikes hit onto him doing maximum damage. This is similar to Crow's effect for his super where he can have almost all of his daggers hit instantly recharging his super by using one super. This is also why spike can do slightly more damage to brawlers with bigger hitboxes such as Primo, Frank, Rosa, and Pam cause she's THICC. But yeah, because those brawlers have bigger hitboxes, Spike can hit more of the spikes from his needle grenade at close rang