Thank you so much for your post, cybmole!
I installed the kepub plugin (it seemed the easiest and safest option for me, lol.) in calibre and converted my books and it's made a huge difference. Margins look as I want them now. I might try Geoff's patch down the road as well just to get some added customization, but for now this has worked out perfectly.
Thanks again to everyone who took the time to reply and also to those who so kindly private messaged me to help even further. I really appreciate it.
