Hello,

You apply the custom size incorrectly: you set only the height. And you need to set the width as well. The custom size would not make different image sizes to be equal, it cuts the images as per the settings: https://gyazo.com/da7ac4b851ec040cedccbd07a5f63c84 I have set 70×70

You need to upload images of the same width and height, and then you can reduce the theme with the custom size to have proportional clear images.

Best Regards