using a water RESISTANT bivy in the rain..?

I've been using a MLD superbivy since 2009 including a PCT thru-hike. So I've been in rain and snow with a strong wind under my tarp with it. I'm a side sleeper and often flip sides during the night. I've never had the bivy roll over. The only danger would be if you camp where water pools and it forms a puddle where you are sleeping. I've actually had drizzle come down on me cowboy camping. One time, I just moved under a big Spruce tree and went back to sleep. It doesn't immediately let water through, it has to saturate the fabric first.

I am a slide sleeper as well but have never rolled around enought to roll onto the WR side of my Bivy. Having said that, staking the loops would seem to be a reasonable option (at least on one side).

of course of you have serious pooling that would be a challenge – but even if you are camped in an ok place still in heavy rain there is considerable water flow on the ground…do you guys use a groudsheet to mitigate that? is the pad outside or inside the bivi?
do you stake out the bivi on most nights?
how do you guys setup camp with such a bivi?

just played with it outside in the yard again…i realize the top fabric isnt that easy to soak…but would be timid re sleeping under a tarp in torrential rain (again – maybe its just psychology

Rain pouring all night. Rain pouring all day. Every flat spot a lake. Every sloped spot a river.
Those are tough conditions which thankfully I haven't backpacked in.

Generally it isn't that bad. Good site selection can often put you on a small bump where water drains away. Maybe the ground isn't even very wet when you set up. It usually doesn't rain hard all night long every night in places that sane people backpack. (Although I would like to backpack in Scotland, that doesn't prove that I'm sane). The typical conditions where YOU plan to travel make a big difference.

People often think of anything less than 100% waterproof being an invitation to saturation and "total down collapse". Sometimes you get a little damp. Usually it's no big deal as long as you can eventually dry out.

Regarding pad/bivy-I like my pad inside the bivy so I don't slide off. That way I don't ever roll the bivy over. Bottom side stays down.

Any Bivy should have a waterproof floor (silnylon), so groundsheet shouldn't be needed for your bivy. Sleep pad should be inside the Bivy. Haven't staked out my bivy before. Only necessary if windy to prevent bivy blowing around while you are not in it. From a packing standpoint, I leave my pad inside the bivy after deflated and stuff the whole thing in my pack. Sleeping bag usually is separated in the pack but could certainly be left inside as well.

If no chance of rain I just throw down the bivy, blow up the pad, put the sleeping bag in the bivy and off to bed. If rain is likely then will put up the poncho tarp but still keep the Bivy to keep off wind blown rain.