My 2 cents: when I played four string I anchored my thumb on the pickups. When I switched to five, I realized that my thumb was now floating. Sometimes it's a moveable anchor: I'll rest it on the string below the one I'm playing. But that's mostly when I'm playing lines that don't move much. When I play fancier riffs, I realized that my thumb floats... it hangs straight down, and mutes the lower strings when I'm playing riffs up high. The more strings on the bass, the more important this would seem to be!
Again, I didn't consciously adopt these techniques, they just happened out of need. I believe I'm a better player now that I don't anchor my thumb on the pickup.