Ive put in many flagstone walks, patios, dry and wet set, and use a
solid base. Dry set is easier and looks better. Use fine gravel dry
setting the stone in dry mortar with a mortar-gravel base. It allows
you the excess time you need to level and place the stones , stones vary
in thickness and wet setting is much harder to get it even with the
limited time alowed. I just looked at one done 20 yrs ago it looks
great. The mortar cures completly from ground moisture and rain. My
uneven jobs are wet set.