ios - PVR compression versus PNG -

i'm testing different compressions spritesheets game on ios. in surprising way, more important memory (ram) use pvr 2 bits alpha instead of png 32 (rgba 4444). consumption 25% higher pvr 2 bits instead of png 32 once spritesheets loaded inside memory. i'm using instruments xcode verify memory use on physical device (ipad air 2)

i'm using texturepacker generate spritesheets.

i've read evrywhere pvr 2 or 4 less memory consumer png 32. how possible ?

edit:

this strange because according observations, pvrtc 4 bits rgba uses lot more memory (ram) png 32, neraly 3 times more according instruments xcode. pvrtc 2 bits rgba 25% higher png 32 rgba 4444. i'm talking live ram consomption, not disque size has nothing , not problem. seems ios manages pvr differently it's supposed do, when loading them ram.

edit2:

my textures 2048x2048, there pot , have square format. evrything work fine, except ram consomption higher should be. make tests physical ipad air 2 device connected mac usb cable. use instruments inside xcode verify , follow ram consumption in live. i've solved ram consomption problem switching png 8 bits (indexed) format texture divided 2 (1024x1024). make scale x2 in code recover normal size texture. ram consumption droped 240 mb (png 8 bits indexed) instead of 950 mb (pvr 2 bits rgba). game video puzzles (with 8 seconds video loops @ 15 fps) , uses lot of sprites. (43 spritesheets in each puzzle generated texturepacker, around 130 sprites in each spritesheet)