3D FlipBook - set flipbook height /padding same for all pdf

Hi, I am using the free version of the plugin. My issue is the flipbook padding is ok with a4 pages, but for other lesser size pdfs the padding or margin is increasing ( mainly from top and bottom control is overlapping the pages. How to fix the padding for all size pdf as same.

https://prnt.sc/1yzo20j

Regards Sumesh