Thumbnails on Home page posts

This is a great theme and t’s very nice to work with. I have a question regarding thumbnails integration in posts on the home page.
For some reason, they either do not show or show much too large.

I also tried different plugins to regenerate the thumbnails, but still they wont show.

I found a temporary fix on this forum :

.blog img.attachment-post-thumbnail.wp-post-image.img-responsive, .blog .entry-content .thumbnail-post .mask, .blog .entry-content .thumbnail-post div.icon, .blog span.thumbnail-post {
max-width: 200px;
}

Now the images show at the specified size, which is different from the setting assigned to thumbnails, which on my site is 170 X 170.

I must point out that the images were imported from another WordPress site. So, is there a setting panel that manages the appearance of thumbnails?

Also, is there a way to make the thumbnails appear to the left of the title and exert on the Home page posts? That would be very cool.

Thank you!