I know I can easily zoom in or zoom out in HAN Software's ePub Reader but if I do this, whenever I re-open my ePub, I have to zoom in again.
Is there a way I can set a static font size for ePub Reader?
Are you using the latest version, as I can see that there is a new release on the 6th of January. You shouldn't have to change the size of the text when you open the eBook back up, as many eReaders save it as a preference. The original size of the text is marked in the CSS.
May I also suggest using different ePub readers, such as Calibre as it is used more widely by the eBook community, and no reports of the issue with having to modify your size settings.
If you are thinking of purchasing DRM eBooks in the future, I suggest using Adobe Digital Editions, as you can still read non DRM eBooks in the software, and it too is more widely known to the community.