Just wanted to give an update on how the bivy is doing in the field after testing it out again. Here is a pic if it in action:
I opted to sleep on the tip of a peninsula of a big lake, and with pretty clear skies I decided to cowboy camp it. It was awesome. As the sun went down the midges and mosquitoes came out in full force, but I lay safe and cozy in my bivy after a nice swim. I could see a small cloud of bugs over my face as I slipped into sleep, behind them several stars peeking through the dusk.
In the morning there was a fog over the water, and I had expected this location to be the place to give me condensation issues, but there was hardly any. At first as I inspected the inside of the bivy near my torso I thought that there was none at all, but when I got up and turned the bivy inside out, there was just a touch of dampness at the very tip of the foot box. Not enough to form drops of water, more like a fine mist, and again--this was only in the very tip of the foot box and no where else. It was dry in a matter of minutes.
So still very happy with the mod, and my bivy/tarp combo is still my go-to shelter for trail hikes. I think that all bivy sellers should have an option to add a vent like this as a standard option.