Poor germination with lettuce / spring mix

Hey, folks.

Anyone grow spring mix (leaf lettuce) for production?  I've been growing it for some time but more than occasionally experience poor germination.  We've had a wet Spring / early Summer here in Northern MN.  I've planted a couple 50-100' beds in succession and have seen both adequate germ in some beds and very spotty germ in others (even ones I double seeded).  I have entire patches where it's as if I didn't sow seed at all.. entirely empty!  I use an Earthway seeder and am pretty diligent about checking in as I'm seeding to confirm that seeds are leaving the hopper.  I'm not finding rogue lettuce plants in my paths, etc to indicate my seeds are washing out during rain events.  I set my seeder at 1/4" in terms of depth.

Wondering if anyone else has experienced this or has any insights.  Thanks for your time.

I no longer bury lettuce seed. Sprinkling on the surface and then watering works very well. I save the seed heads and in the very early spring shake them over the garden. Usually get way too many, a solid cover of lettuce, which I thin to use as mulch.