How can I make a slideshow gallery height responsive for mobile?

Hey guys, I have the following problem: My Slideshows looks great on desktop, but not as good on mobile, especially for portrait mode pictures. For landscape, it is fitting but the pictures in portrait mode are too small (high). I want them a bit bigger. Is there a possibility to do that?

Please take a look on this homepage for instance (on mobile): www.tobiasholub.at

Thanks for your help!Michi