I have hunted with four different PHs, none of whom would let me shoot at a plains game animal laying down (unless it was wounded), let alone buffalo. Maybe I had an opportunity at two different buffalo laying down. Both times it was wait for them to stand. Both times they took off as soon as they stood. I held fire the first time because no shot presented and also told not to shoot: buff ran straight away. I shot the second bull running through both lungs at sixty yards. Wasn't told not to shoot so I took the shot. PH said later he was confident in my ability to make the shot. He'd seen me in action with running shot on previous safari. And that gemsbuck was a much more difficult presentation than the buffalo.
Offhand I can recall over the years shooting two moose and one whitetail in their beds. One bull was less than twenty yards in very thick alders. So thick I couldn't see the cow standing ahead of him (though knew she was about). It was nearly dark and I easily put 180 gr 06 through his heart. Close enough I could have thrown my gun and hit him. Snow was almost knee deep so tracking would not be difficult: I'd been tracking them all day. He got up and ran into a spruce tree maybe fifteen yards away. I could see it's top disappear and noise ceased so I knew he was down. Second bull was asleep in a cutting unit, just before noon. Again, deep new snow. Watched him from eighty yards for quite a while before the sun lit up his rack and I could tell for sure he was a bull. Very deep snow and laying sideways so I took a neck shot. He stood up sick so I shot him in the neck again, knocking him over. That was a mistake. Should have put it in the boiler room. Wound up shooting him five times before it was over. Three bullets would have eventually been mortal and the fifth was a brain shot as he turned for me. Fortunately, he didn't go far or suffer too long. And I maybe only lost a couple pounds of meat. Lucky there. Without snow I would not have taken a shot till he got up. But without snow it's doubtful I would have seen him till he was up and off. The whitetail buck was laying over the edge of a bench peering down at me from maybe sixty yards. No snow. All I could see was his head. So I shot him in the head. He would either be dead or the shot missed. If I missed, no big deal. No worries about wounding him. Still early in the season and he was far from being a trophy. Meat in the freezer and not an ounce wasted.
I suppose there are some situations where shooting a buffalo laying down might be acceptable. Firstly, the PH would have to be confident in the shooter's abilities. It would have to be an absolutely open shot which would be difficult because buffalo tend to bed down in thick stuff. Shot placement would be atypical because buffalo, like cattle, seldom lay down with body vertical. They lay tilted on one side. Consequently, trajectory after impact may be angled. PH needs to know how to adjust for that ... if it can be adjusted. Basically, the shooter has a better view of the vitals if the animal is standing. Better view = higher probability for mortal shot placement. When dealing with dangerous game, shoot for the highest probability for lowest bad outcome. That's just common sense.
