I also replied on github, but yeah, that's unexpected. I remember it working for me 8 years ago (although the actual laser gun accuracy wasn't great, probably due to me using KallistiOS' light gun stuff wrong).
With flycast actually working with my game, I'll try if I can figure out what exactly was off about the lightgun code. Unfortunately can't give an ETA for that right now, getting Mirklings up and running again is probably a bit of a compatibility nightmare with the newer engine, but I'll have to actually check it out first. Thanks a lot for taking the time to share your findings here and on github!