You should connect your blue gauge to the compressor suction line (where you indicated 25° on your drawing). For superheat calculation you need the pressure from there. The pressure at the current measurement point (where the yellow hose connected) is irrelevant.
Your metering device is capillary tube. Most probably it's built together with an antiparalel check valve wich let the refrigerant flow free in reverse direction. You need similar thing front of BPHX for the planned defrost operation.
T.
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