Henry is a very knowledgable guy, I think he's just jarshin me.
If you make that ledge up just a half inch or so off the bottom then you make the moulding so that it covers it, there you are back like it was originally. We will have to think about how to make that moulding. I imagine something could be done with the original window frame, cutting the back off leaving a lip all the way around that can stick down into the channel, holding it is the issue. If you did this of course you would need to leave more room around the window so the channel didn't fill up with urethane as you would want with the S-10 style moulding, that urethane filling the channel is what holds it.