Compression of jpg Sprites not working

Dear Community,

in my private project I have a lot of sprites. When I built my game I used the editor log to look at the size of my assets.

A bunch of these sprites end up as assets with 2.3 megabyte and a few others end up as assets with 360kb. The only difference between these sprites that I found is the warning in the inspector:
"only textures with width/height being multiple of 4 can be compressed to DTX1 format"
Looking at the size of the jpgs in the assets folder of my project I found that the resolutions of my images are very different and barely any of them have the required 'multiple of 4' relation.
Here is what I found:
The images that are compressed have ratios of:
- 755 * 1051
- 756 * 1052
- 752 * 1052
- 755 * 1056
The images that are not compressed have ratios of:
- 755 * 1055
- 756 * 1051
- 755 * 1052
- 752 * 1051

Can anyone explain this behavior? I am utterly confused. And since my project of only a few cards has 500mb I want to reduce that size.

 

I ended up simply doing what Unity recommends and altering all images to a width/heigh ratio multiple of 4. The confusion about what I described above remains. However the image compression works now. My game is now 180mb instead of 500mb.