Effect of depth in an echocardiography when retreiving distances of a segmented region

I have an echocardiography image where I want to segment a region inside it. At the moment I have been able to segment the part of the image I want, callibrate in order to get the real distance of the segmented part, and I have also been able to get the x,y real coordinates.

My question is, does the Z (depth) affect the real distance of the x,y coordinates of the segmented part of the image? I ask this because I don't think is the same getting x,y coordinates in a depth of z=5 mm than getting some x,y coordinates at a depth of z=7 mm.

The depth values (Z coordinate) in the MRI image is shown by the yellow line, this values are real distances.

Thank you in advance.