Sprite Packer weird sizing?

Unity 5.4.2 pro + Sprite Packer
Sprites : FULL RGB game background maps (no-alpha)
Platform: Android/IOS
IOS: only support POT square atlas


I have two sprites of size 512x1024 which am packing into one sprite atlas using single tag.
Instead of creating one sprite atlas of 1024x1024. Unity is creating 2048x1024 atlas on android and 2048x2048 on ios which is doubling the size.
I've tried all three packing policy and different sprite import setting but nothing work.

If I pack two 1000x500 sprites, it does pack in 1024x1024 atlas.

How can I simply pack two maps of size 1024x512 into one 1024x1024 atlas which works on ios as well?

atlas with 512x1024 sprites in ios become 2048x2048



Atlas with two 500x1000 image packed into 1024x1024 on ios


What should be ideal game background/map size to effectively compress on both mobile platforms?

 

Ping, any help please !!!!!

 

I don't use sprite packer, but other packing software usually add a padding value of 1 or 2 pixels around the border of all sprites, so this would push you over the 1024 x 1024 limit. I'm not sure if Unity lets you adjust this padding value, but the software package I use, TexturePacker, does. Although, removing the padding may lead to bleeding effects, but I've never tried it.