Hey Cottima,
first of all, thank you for the purchase, glad you like the theme :)
Regarding your question: the height of the portfolio boxes on mobile screens is determined by the height of the standard 1×1 box in Ikebana, for multiple reasons. However, in your case since the 1×1 box is quite small, I would try removing this rule: please download this custom archive I’ve prepared for you, unzip it, and upload the contained file into the theme folder (/wp-content/themes/Ikebana), replacing the existing file. Let me know if it improves the situation!
Best,
Andrii / Satori Studio