I like your description -- relaxed propulsion. Gotta use that.
I just got back from my lesson. We spent the day working on legs. (Did I mention that this new coach is the best thing that ever happened to my dancing? 8) )
Anyway, the conclusion I've come to is that propulsion is exactly right. You propel yourself through space. But relaxed? Nope. No relaxation at all. The relaxed look is an illusion. It's like that old analogy of the duck floating on the pond, looking tranquil, but underneath the water's surface, paddlig furiously.