Ahh, yes. In the coordinates room, perform that operation, then on the left side there will be a field named “dist” that will have a value of something like 0.0, click that and enter a number (any number really, as long as it’s consistent across your shots).
For further reading/insomnia remediation, here is the relevant page from the the beloved Syntheyes manual:
https://www.ssontech.com/docs/SynthEyesUM_files/Size_Constraints.html