Finding player hitboxes/modifying collision detection in Blitz 2000

[blitzmaster5000]

I was wanting to try and modify blitz 2000 to have the stiff arm do "splash damage". In essence, something as simple as increasing the radius of the stiff arm hit box is all I would need to do I think, although I'm not sure how the game handles collision detection. I have found addresses related to the stiff arm move itself, but modifying these functions doesn't do anything related to what I want to do (basically just modifies the animations, not the actual action itself). Does anyone have experience with other games and how they handle collision detection? I would think that if it's possible to modify the player hitboxes (increase their size), this would essentially give me the result I'm looking for.