Large size is set to a high value, but I can set it higher. It should be a 20% larger than medium size. In my phone medium and large look the same too, but my screen is small. I expected to be a diference in high dpi phones like yours, but I couldn't test it.
Thanks for reporting, these ypes of things cannot be tested without a comunity like XDA, I am really grateful for all the tests and reports I am getting. I'll check it, and I'll try to fix it. It seems to be related to the notification aspect ratio. The ones working best are the ones that are slightly taller that wide.
One problem is that the icons can never be larger than the notification heigth.
I also know that now that the "X" to remove contacts is so small, it is very difficult to hit. I'll fix it also.
Here's another feature request:
Add an option for spacers between images / contacts. The icons are so small on my phone that it is a little hard to hit the right contact photo. I tried just adding 3 contacts into entries 1, 3, and 5 but it still crammed them together. Could use a few millimeters between each photo.