Projectiles very laggy

Hello! I'm trying to create a throwing bomb that explodes on impact for an alien mod (in which the UFO's and player will throw at each other). Everything works fine whenever the playing throws the projectile, no matter how many projectiles they throw, but whenever I have the UFO throw it, it tends to lag out the game. The UFO sight range is 32, which I don't think is too big. I can give more information if you'd like, thanks.

Edit: I found the cause of the problem. The UFO hitbox used to be 6 blocks long and 3.5 blocks tall. When I set it to 0.8 blocks wide and 0.6 blocks tall, the lag stopped. But I need the UFO's hitbox to be that big so the player can fight them without anything phasing through.