Don't get me wrong, I have nothing but love for the rounded back version of Paschimottanasana. It holds the patent for the the yummiest adjustment ever. (Disclaimer: I hesitate to even call it an adjustment since it's not something you would offer to many people in a class setting.) It's the one where someone sits on your sacrum, facing away from you, presses into their feet to push your chest forward, and then essentially sprawls out over your spine using their own body weight to melt you down? This is similar to a partner yoga favorite, where people sit back to back, butt to butt and one folds back while the other folds forward, but I find this variation to be much, much deeper... In fact, without relatively open hamstrings to begin with, I doubt it would even feel good. Your face ends up smushed between your shin bones in way that would appear decidedly unpleasant to me, had I not confirmed it's appeal!
Obviously, I would only use this if I knew the person and their practice well. But in terms of deepening a forward bend, it's pretty much the cat's meow! If we lived in the same city I would come over right this very second, put on a pot of coffee, and gingerly plop myself down on your back to show you!
I am absolutely intrigued as to the 'stuff' that is being dredged up by focusing on not collapsing in your forward bending? I remember hearing in a lecture on the subtle body, that deep forward bending can be very emotional as it opens the backs of each chakra instead of the front... but I've also heard that the chakras radiate in every direction with no specific front and back... so who knows. I am fascinated. Tell me more!