Interstitial Ads question in Unity with using Admob

[Supreme Studio]

Hi

since interstitial ads shows the top of the UI, does it automatically decide it will go always top of the UI? or I need to adjust sort order to the top?

I am using Unity to create games and also implementing Admob.

here are my questions.

1. if I use game UI which is placed sorting layer as 0 in unity, should I change sorting admob sorting layer to 1 so interstitial ads are opening always on the top of each UI?

or I don"t have to change sort order which is 0 because admob automatically adjust for us? it looks like OK to me when I play my game and display ads which shows always top of my UI.

2. which are the better solution for displaying interstitial ads?

 a. when the interstitial ad opens, all game UI should be turn off.

 b. I adjust sort order in unity like 0 for default and 1 for in front of all UI.

3. if I can adjust sort order in admob, how can I do that in code wise.

it is just because admob policy center call me up and said there is a problem covering google ads (I am not sure where that is because they don't specify where..., so I suspected interstitial ads)

anyway, please kindly someone tell me how I should handle.

thank you

Shota