For high temp cooks like pizza and searing steaks, etc. I leave the lid open until I have a pretty good flame and hot bed of coals going. When I close the lid I really have to watch and control the lower vent so I don't overshoot the temp. I think maybe you're not letting your coals get hot enough. Of course wind and other things can factor in, but mediums have the same size lower vents as larges so that has to be it.

Mike

Know fat, know flavor. No fat, no flavor.

I tried going vegan, but then realized it was a big missed steak.