Hmm, the canvas used for the format conversion should scale to the natural dimensions of the image, but it sounds like there is some enlargement factor that I missed with those. So I can test the problem site, could you email me at jscher2000@outlook.com or submit a new issue on https://github.com/jscher2000/Save-webP-as-extension/issues ? Thanks.

As a workaround until then, you can try the "IE11" button, which re-requests the image as an older browser to discourage sending modern formats. Depending on the site, that may work for you.