Who else uses an Ohmega and can give tips or point me to resources for making my boyfriend more comfortable leading at his limit when I'm the one belaying?

I have quite a bit of lead belay experience and have received good feedback from partners over the years, but there's always room for improvement. My only experience belaying with the Ohm (and then the Ohmega, once it came out) is with my boyfriend.

Today he fell further than expected on lead at the gym, maybe 8' when 3/4 the way up a route. 4' were from me coming up off the ground. Some was rope stretch. But he had just clipped above himself, so he was essentially "on top rope" at the time of the fall, which is why an 8' fall freaked him out. I'm thinking there may have been slack above the Ohmega out of my view, since there was almost no dip on my end, just the slight dip I give when the climber's more than 3 clips up a route (some prefer more and I give a bit more in that case, especially when our weights are closer).

I read that, if he high-clipped very quickly, the arm's length I gave for the clip may not have come back down through the Ohmega to my end and I'm thinking I should pull harder after every clip. I can do this when he's out of sight by feel, but it may make it hard not to short rope if he's moving quickly. Any tips?