No Co-registration to subset

I am using SNAP 3.0 to perform InSAR on R-2 images.
Since there is a lot of water in the scene, I am subsetting the Master to a purely terrestrial region. Now, the tutorials indicate that I can perform coregistration between the subsetted Master and an appropriate Slave.
I run Coregistration and things happen. But there is no data in the coregistered slave products. Do I need to subset the Slave as well? And if so, how?

no, you shouldn’t have to subset the slave. It could be that none of the GCPs are within the warp RMS threshold. You could try relaxing that a bit or in the Cross correlation add many more GCPs.

In the resulting product, you can see the RMS values and shifts for each cross correlation window. Go to View -> Tool Windows -> Radar -> Insar Stack.

I relaxed the coregistration requirements, and got a “coregistered” slave image that could at least be seen. But it had no spatial relationship to the Master. Following your guidance above, I get the message: “This tool window requires a coregistered Stripmap stack product to be selected”
So using Coregistration parameters that permit coregistration of the full Master and full Slave, I am unable to get anything meaningful in Coregistration, after performing a Subsetting of the Master.
I guess I can proceed without subsetting, but it seemed like a nice feature.
Thanks, Don