Hi. To be clear, it's the "Float Fish" line. Supposed to sink a short way beneath the surface. Which the 4lb example does, requiring a bit of rod tip assistance. The 6lb version, as I said, is as prone to floating as anything else among the countless lines I've used.
Given that surface line drift is a perennial, troublesome, effect when fishing still waters, it would be good to find a line that sinks a little more reliably. Could it be that the "feeder" version of these lines, which are also claimed to sink reliably, would actually be more suitable for float fishing? Not that sinking the line has ever been much of a problem to achieve where using feeders is concerned in my experience.