What is the boundary condition you have at the inlet? Is it a velocity or a pressure?
The inlet pressure boundary condition is a total gauge pressure, meaning this is measured against the operating pressure that you are using. Therefore if you define the pressure as 1 [bar], this is actually 2 [bar] absolute (assuming default opeating pressure). When you change the opeating pressure to 2 [bar] the inlet pressure would also adjust to have the value of 3 [bar]. Maybe this is why the contours look identical.
If you defined the inlet as a velocity, the absolute pressure at the inlet should increase.
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