What is the best way to convert the result to mobi/azw3?

[KaMyKaSii]

I have the Kindle Paperwhite 4 model. When I process the images through Mangle and convert them to mobi through Calibre, even if I select not to process the images again, the result seen on the Kindle is images centered on the screen, none of the edges of the image touch the edges of the Kindle screen. Is there any way to get a result similar to KCC, with the images taking up as much of the screen as possible but without distortion?