Your starter is the one piece that touches land, so it is the piece that has to suit your shoreline rather than your dock.

Seawall

A flat vertical face is the easiest case. Mount straight to the wall and set your height once.

Sand and gravel

Use a footed starter and let the legs carry the load. Re-check height after the first week as the bed settles.

Rock

Rock rarely gives you a level bearing point. Plan on adjusting each leg independently.