Make all thumbnails 4 x 3 dimension?

Hi there. I am trying to make my thumbnails a consistent 4×3 dimension but am having a problem. The plugin is creating/using an auto-generated thumbnail that is 150×150 (how is this being generated?). Thus, if I use a big picture (say 300 x 225), all is good b/c it uses my properly sized thumbnail. However, if I try to use a dimension around 150, it defaults to this auto-generated thumbnail that is 150×150 and so I can’t get my 4/3 dimension that I am looking for (even when I set this in the plugin it still does 150×150.)

How can I make all images in RPWE have a 4×3 dimension? (I have already made sure that all “featured images” are of a 4-3 ratio.)

Thanks in advance,
Richard

https://ww.wp.xz.cn/plugins/recent-posts-widget-extended/