Duragrouch: you can get 15-84" on a folder, but not with the Super Short - it has 39t tensioning capacity, and the configuration you mention needs 47t. I don't know of an RD usable on folders with that rated capacity, but 43t can be had with Shimano's Smart Cage siblings, Tourney TX-800 and Altus M310. That's enough for this:



Allowing rattle, their capacity is 47t, but unfortunately their max cog is 34, & I tested that on another pseudo-cassette, & wasn't able to shift onto the 37t, even with B-screw maxed.

Smart Cage is a clever trick that permits that whopping 43t capacity with reasonable ground clearance. Here's BF's take on it: What is shimano smart cage on a rear derailleur?. The Altus is the better of the two - metal body instead of plastic, and due to an exceptional 15t lower pulley - you can see how huge that looks on a derailleur as it's fondled on this 48-second video
even better clearance than the Tourney; it's Grant Peterson's all-time favorite RD, shipping on lots of Rivendells.

Regarding 20t gap on the front, it can be done; I ran 28-48 on my Dahon for 2 years, using a Tourney FD I hacked up (because clamp was too small for Dahon tube) & attached with hose clamps, and Sheldon Brown used to rock a 51/26:



Regarding conservative ratings & the hidden powers of cheap derailleurs, you might enjoy a deep dive thread, entitled What Shimano doesn’t want you to know about the $12 Tourney TY-300. Eating this 11-40 1x for breakfast, in the XBiking subforum of a site whose name I believe we're not allowed to speak here.