I understand your equations and I also understand fall factors. I am also a qualified climbing guide with over 10 years experience of taking climbing falls in many, many different situations. In an ideal world you may fall how you are expecting...however the real world fall may be quite different to what you may expect.
If you need any roped assistance on Broad Stand then the only safe way is either a top or bottom rope (or course leading it).
I will correct you by saying that it IS very easy to snap a sling and the nuts in a situation like you describe.
Sure I get what you are saying about the fall being more of a penduluming slide than a true lead fall....however you are getting into very, very dangerous territory by climbing above a piece/pieces of gear on a sling (or short section of dynamic rope). Slings WILL snap with even a short fall directly onto them - in fact climbing above a sling is one of the most dangerous things you can do in climbing.
DMM have done a very good video demonstrating this exact scenario - if you don't believe me