OK, I get it.... there is an odd behavior in Hovermate.... once you write an image width in the Hovermate stack, you can't delete it. If I try to delete it, it defaults to 100px. So I dragged a new Hovermate in and it worked responsively. Thanks a bunch.
Also, fwiw... not sure why, but in Safari when I scrub the window size from large to smaller (and visa-versa), your demo page strobes back n forth to full white. Then entire page strobes, which is seizure-inducing Just thought you should know.
Anyway, thanks for all your input, much appreciated.