With the excessive thickness (2-1/2") instead of the recommended 1", the pavers can "float" and suffer differential settlement or rocking due to moisture under the pavement. Polymeric sand will not be a long term help since the moisture can come from the base or from the side.
The setting bed sand should be a screeded and not compacted uniform and a uniform 1" thickness. Any drainage (if desired) should be taken care of of with surface contours of the compacted base, but setting bed must be a uniform thickness.
These are normal installation for all interlocking concrete pavers (not the larger (12" or more wide or long) stepping stones that are of highly variable properties and strength with no standards, while the interlocking concrete pavers are much stronger (over 8000 psi) and how much you deviate with the installation is up to you.