I completely agree with Jazilla and making this raincoat to fit my down underquilt to the chrysalis bridge without having to use a tarp is nothing but a comfort issue based on preference. Yes a pad is perfectly possible in a chrysalis since it's so flat, but I prefer laying directly on top of the hammock fabric with an UQ attached.
As Jazilla said, there's people that love pads and then there's people that don't. I'm one of the latter.
As to the flatness of a bridge, look at the bear mountain bridge, not much flatness there as in a "bed like surface". Mostly what is meant with bridge flatness is the fact that you can get a flatter lay in them. Not that the bridge itself resembles a flat surface. There are of course exceptions that also have a "flatter bedlike surface" to boot. Like the chrysalis and Ber's cyrus or cloud DIY bridge.
I'll be adding a step-by-step guide as to the construction of the UQ raincoat in the run up to the actual test. After field testing, I might still change some stuff.