Page loading speed and image optimisation

Hi! When I go into my hub and do a performance test, I am still getting less than 5 out of 100 for 'optimise images'. I have smushed every image on my site, including using the pro features, and also manually re-uploaded some photos which remained untouched by Smush. I believe I've checked every single image and they are all 1MB or less, in most cases, much smaller. I don't understand what I'm missing and would really like to sort this issue out. Thanks!