Hmm... I've really only been targeting my primary test mediums... 'kindle pc' and ADE. (I loathe to bring out my ancient first gen kindle, and I mourn the death of my android machine)
But if just 'making it work in the software' isn't good enough, I guess I'll have to trust resources like the link you gave.. well.. that or the publishers themselves, I guess. (I'm assuming they give target specs during submission)
Bleh... I made the covers myself (originally for 6x9 print, mind you) so if I'm forced to resize and adjust for every venue I attack, I'll survive.
Thanks for the tip, onward I go...!