Most DIY instructions I've seen say to install the sprinkler heads just a little bit ABOVE ground height. Dirt builds up over time. Some of it is dust that settles out of the air, some of it is leaves, grass clippings, and other things that organically decay over time. The build up isn't fast. But if you mount the heads perfectly even with the ground, in several years from now, they will be below ground level.
I would suggest a mounting height of 1/4" That will give years (decades?) for soil to build up, yet high enough than even a lawnmower blade set at 1" won't hit it (assuming level ground).