As you might have noticed, some icons are huge and others are tiny on the StackExchange HNQ page (aka the main page). Here's a userscript that fixes this issue:

// ==UserScript==
// @name         StackExchange Hot Questions fix site icon size
// @version      1.0
// @match        https://stackexchange.com/
// @grant        none
// @run-at       document-end
// ==/UserScript==

(function() {
    'use strict';

    [].forEach.call(document.querySelectorAll('.hot-question-site-icon span img'), function(img) {
    img.src = img.src.replace('48','32');
    });

})();