Compression vs. turbo pressure

Before i changed my head gasket (1,2mm) I had steady 0,5 bar pressure on gauge
now when its 2mm gasket up,i have barely 0,3 bar.

My question is,if I have bit lower compression now,should pressure be the same?

By fitting thicker head gasket, you have reduced your compression ratio.
So this mean you can increase or need to increase your boost to get same as before.
You have more volume than before in your chamber.

Cheers
Atchi

Thank you very much achi.
I was thinking same way,just wasn't sure,so it is better to ask.