I'm keyed in on the statement "no rain is expected." How predictable is that in your intended area? I ask because it seems up in the northeast I can almost surely count on some overnight rain even if it's not a high probability in the forecast. Maybe my perception is a little skewed, but I will always account for it up here.
But if you're in an area that truly doesn't see rain or has a dry season where the chances are truly low, I'd skip the bivy and liner and just bring a down bag. Probably the same bulk, but you wouldn't have to worry about being cold. And if you did get hit with rain, just pack up and head out. You said it was a short hike in. Bring a good headlamp!!!
Bugs might be a concern with my suggestion. A headnet may or may not work in that case and perhaps you truly can't leave the bivy behind.
So to me it seems like you're almost guaranteed to have to worry about being cold with your setup, whereas with my suggestion you don't have to worry about being cold, but have to worry about the small probability of getting wet.