A terrain calibration piece should reproduce the system’s real interfaces, isolate likely failures and give users a fast pass-or-adjust decision before a large print run.
A slip fit allows movement or removal; a press fit holds parts together through interference. For FDM parts, the correct dimensions must be proven under final print conditions.
There is no universal peg-and-socket clearance for FDM parts. Define the gap correctly, print a calibration coupon under final conditions, and verify the fit.