When I set texture to ASTC in Unity-texture-importer, which "GL format" does unity apply?

Hello everyone, I got a problem about ASTC.

I use "Mali graphic debugger"(MGD) to test if Unity's ASTC format was really works for Mali devices.
(My device is HUAWEI H60-L11, GPU is MALI T628MP4)
I tried several ASTC format in Unity(ASTC 4x4 / ASTC 6x6 /ASTC 8X8/ ASTC 12X12)
But when the game running, MGD showed all of them had been decompressed to RGBA.
This cause a waste of RAM usage.

For comparing, I debug blizzard's hearthstone in the same way, same devices.
MGD showed many texture‘s format is "GL_COMPRESSED_RGBA_ASTC_6x6_KHR", but not RGBA.

I don't know how hearthstone compress their texture, maybe it use some other ASTC tool instead of Unity-texture-importer, but I've no idea to verify anything.

My question is :

1) When I set texture to ASTC in Unity-texture-importer, which "GL format" does unity apply?
I found a lot of GL format in this link https://www.khronos.org/registry/gles/extensions/OES/OES_texture_compression_astc.txt
GL_COMPRESSED_RGBA_ASTC_6x6_KHR is one of them. Which "GL format" does unity use?

2) How to compress texture to "GL_COMPRESSED_RGBA_ASTC_6x6_KHR" with Unity?
The purpose is to prevent device decompress is to RGBA when game running in MALI devices.

 

The result above was got from Unity 4.6.6p2.
Today, I did a same test in Unity 5.1, I found ASTC4x4 could be loaded on devices, did not be decompressed to RGBA. I think it's a bug of Unity4.6.6p2.
Did anyone experience the same problem?