You are right - on a recumbent you may have to adapt other strategies. But that's fine - the concept still applies. So, lets try this again.

Motorists have one overriding (no pun intended) fear of you, the cyclist: you are going to do something stupid to place yourself in their path.
Yes, I said "fear." They may get angry that you are in their wa,y on "their" road and may, on rare occasions, slow them down. They may question your sanity that you are even out riding on the open, paved roads in the first place. But they fear you may turn in front of them and they wont be able to react in time. Or that the lane is too narrow to allow sufficient clearance for both of you. Either way, they are socially and culturally conditioned to NOT hit you.

The head check is a way to signal to the driver that you are paying attention and won't do anything stupid... in a very real way, it helps soothe their fear of you.
For a moment, lets take this out of the realm of the esoteric and look at it from my perspective.

I ride solo for fitness, mostly out on open country roads. Out in the boonies, cars are fewer, but they are generally moving fast and there is a long reaction time available. Here's where the head check comes in. You may have missed it earlier, but I have painted the SIDES of my helmet in fluorescent colors. When I turn my head, drivers can can see my head turn as a bright color anomaly on the road ahead. It is something like a warning beacon, you might say.

So, motorists first see me as a "blob" in mid lane, because I ride in the half, to one-third lane position. As they get closer, they see my head turn, as I take notice of them first. I hear them coming and I see them in my mirror. Then they see me wave my hand once I've seen them... they may not know why, but they see it. Next, they see me negotiate the lane in their favor where practical, because I saw THEM coming and have the time to make corrections. They know that I am paying attention - in some case, maybe more than THEY are.

I also DO NOT ride with a personal music player/earplugs blasting in my ear. You need all your senses on the road and your hearing is tres important. I use a mirror, too, and check it every 5-10 seconds for approaching traffic. Meanwhile, as I noted, I take the lane where ever practical and work from that most visible of positions. I am always keeping an eye out in front of me, as well. In congested areas, these same rules apply - magnified in importance.

All right, back to the esoteric. The point in all of this is the head check is one part of a greater sense of road awareness, the realization that you must be seen in advance, so others can adapt to your presence. It works well, because I take advantage of the reaction distances involved. But, this mindset can be adopted anywhere you ride. I also drive a car and I see cycling from the motorists perspective. I talk to fellow motorists about cycling, too, and what they think of it. I don't do this to push a personal "cyclists agenda," but to learn what THEIR perspective is.

We can howl all we want our equal rights to the road under traffic laws, but the fact is you are not alone out there - you are sharing the road. If the laws also see us as vehicle operators with rights to share the road, then we have to act like it.

As for the difficult-to-see recumbent, do you use flags, bright colors, strobes and other high visibility devices?