Interesting article. I tried that trick but applied auto to the height and left the width to 100%. I didn’t get any better results.

I have this same issue posted on adobe’s indesign epub forum. I got an interesting remedy that I’m about to try. The short end of it is:

1 – Apply inline images
You can start to apply images inline (inside text frame) instead use custom anchoring

2 – Use VH unit
For portrait images is a better choice use VH (viewport height) as unit instead %, like this

img {height: 98vh;}

3 – Media query
Have you try repeat or change some CSS properties only for Kindle readers. You must use media query

@media amzn-kf8 {
img {height: 98vh;}
}