With the newer Panaracer folding tires (Pasela, Gravel King) the rubber is very tacky around the bead, which makes them difficult to slide over the rim lip when the tires are new. It's not that the tires are too small, they're just really difficult to slide onto the rim.
For 50 years I had gotten by with using baby power to mount new tires, but with these new Panaracer tires, I've had to start using liquids to overcome the tacky beads. I used olive oil on one set of tires, and soapy water (probably a better option) on the second set. Someone mentioned using the soapy fluid that's sold for blowing bubbles.
I'm reminded of the old "Grab-On" foam rubber handlebar padding that everyone used to use in the late 70's. I used to use shaving cream to slide that stuff on my bars, the new tires are pretty much the same way, you'll need some help, preferably something that will dry out soon and not leave a residue.