Minifrontpage (free): Thumbnails are not resized

Maybe I wasn't clear enough because of my english.
The plugin has an issue with the sizes. It does not serve what it says. I want to serve thumbnails with specific size (550x300). If I make the sugested adjustment it will be smaller in the webpage. 
In other words, I have an original article image which is -lets say- 1000px700. I wanted to be exactly 500X300 in the minifrontpage carousel. It shows that it is 500X300, but it is actually much bigger even from the original.  the plugin is creating a thumbnail larger (in dimension and in bytes) than the original image. This doesn't  pass several performance tests, as I ve already said. Thumbnails are supposed to decrease the data size of a webpage, not the oposite.How Lighthouse calculates oversized imagesFor each image on the page, Lighthouse compares the size of the rendered image against the size of the actual image. The rendered size also accounts for device pixel ratio. If the rendered size is at least 4KiB smaller than the actual size, then the image fails the audit. # Strategies for properly sizing imagesIdeally, your page should never serve images that are larger than the version that's rendered on the user's screen. Anything larger than that just results in wasted bytes and slows down page load time.

developer.chrome.com/docs/lighthouse/per...thouse&utm_medium=lr  

yES!
That's perfect!
Thank you!