Not sure I understand it fully.
Did you mean that only one data block was showing (and one shielded) ?? Or just that they were directly on top of each other causing difficulty in reading the labels ??
2000' vertical separation is double that required so it wouldn't give me any heartache.
The only problems I have seen with closely spaced aircraft is corruption of Mode A and/or Mode C as the SSR receiver adds both responses together.
If it is a major concern to you, then ask one of the pilots to offset by one mile. Most modern FMS aircraft can do this in a couple of button pushes.