You know, using WebP format for the images will significantly shrink download size, without causing much in the way of picture quality loss.
Just a thought, for more info, ask one of the greater Developers. Like Naughty Road Productions, or Droid Productions. They know how to minimize file size, while maximizing output.
The files are already extremely small. They just use a different image for each slight change in expression as opposed to switching between a few images or employing masks to reduce file size. If you go through each image you can see very slight shifts in camera angle or mouth/eye/eyebrow position such that no 2 images are exactly the same. However the same effect could be achieved through the use of masks as previously stated and result in drastically reduced game size, with the added benefit of masks being reusable between stages of progression.
For example, there are several events where there are about 3 or 4 base positions for the characters, each one being the result of either a shift in camera angle or arm position or a head tilt. For each position, there are let's say 15-20 variations in facial expression, usually with variations in eye position, mouth position, blush, or eyebrow height. So those variations will result in say 50-80 separate images, the average of which let's say is 225 KB. Each individual event would result in 12-15 MB of images. If masks were used, you could have those 3 or 4 base positions, then 3 or 4 masks for each eye, mouth, blush, and eyebrow variation. Let's say you had separate masks for each position, which may not be necessary depending on how they overlap. Each mask is let's say 20 KB. That would make each of those 12-15 MB events 1.5 - 3 MB. Given that there are I think a few hundred iterations of such events, that would probably cut the size of the game to maybe 1/8th of its current size leaving everything else the same.
I know I've mentioned this before so sorry if it seems redundant but I didn't get into that much detail last time. I'm not expecting anything to change but just providing context for people wondering about the file size and maybe some feedback for future offerings.