Thumbnail image cut

Hi,

I have a problem on my website where i use master slider.
I have to publish image with a different size, vertical and horizontal photos.
After a lot of attempts I find the correct setting for the slide but unfortunately I don’t find the correct setting to have, in the bottom thumbnail, the image correctly resized: i see the horizontal one correctly but all vertical image are cutted.

How can I set my slider setting to resolve this problem?

This is a very silly problem but I try to solve it all yesterday afternoon and evening and I dont find the correct set 🙁

https://ww.wp.xz.cn/plugins/master-slider/