I recently dry-laid a ~450 sq. ft bluestone patio in my backyard. The pattern is a mix of large irregular flagstone and smaller tumbled bluestone. The stone is laid on top of a 3" of compacted base and 1-2" of construction sand. I then filled the joints with more sand. My problem is that the smaller tumbled bluestone occasionally shift when I step on them or place a chair leg on them. I realize now that maybe the smaller pieces were too small and I should have opted for larger flagstone, but that ship has sailed. Do any patio experts have recommendations for how to correct this? I am considering replacing some of the joint sand with top soil and planting thyme, sedum and other groundcover, thinking that it will hide the imperfections and hold the stones in place. I'm also wondering if stone dust will hold better than sand in the joints, but I don't want to compromise drainage, which is the reason I dry-laid the patio in the first place. thanks