Sure if they can't.
And if they can, it's a gentle recommendation.
I would dream of a service where one could test the display of his EPUB to sort this out. For me, I have only Calibre, ADE (1.73...), some common Android readers, Azardi and my Kobo Glo (v. 2.8.1. and patched)
Also, as I supply PDF with both formats (9x12cm and IPAD), it can sweeten the pill
if need be, which really I don't know.