[Zubersoft]

It probably depends upon whether those readers are scaling up the page to fit the available width vs showing the page in its original dimensions.  I just looked at the PDF you uploaded, and the first page has dimensions of 34.43 x 48.72 in, while the second page has dimensions of 8.26 x 11.69 in (I can see this in Adobe Acrobat). So that is why you are seeing such a large discrepancy between the two pages. When I am exporting a PDF and have to create a brand new page using a generated image, I scale the image by 300/72 (300 dots per inch divided by 72 pixels per inch to get dots per pixel). This results in a larger image being used which is then scaled down in the PDF when it is displayed on the monitor. I found that this greatly increased the quality of the images in the PDF. Unfortunately, those images are not compressed, so the PDF is generally much larger due to this. 

If you uncheck "Draw highlights behind content", then your page sizes won't be changed at all. This is because I'm able to embed annotations as actual PDF annotations versus having to generate new images for every page where the annotations are drawn behind the content (which is not possible with normal PDF annotations). So you will have to decide which is more important for you.

Mike