Why not a floating towed array?

Why do sub not have a floating towed array? The ones in real life sink below the depth that the sub is travelling at to be able to hear other submerged contacts that may be behind them or below them at great depths. BUT, when there is a convergence zone and you pass below it you can now no longer hear what is above you in passive sonar. Things just vanish from the screen once you pass that 'specific' depth. So my question is why not have a towed array that floats upwards to be able to hear what's above. Of course this would require travelling at slow slow speeds as to not "drag" the array in a straight line behind the sub much like the standard array does when going at high speed. The purpose when using one is to go slow and let it sink to be able to hear what is deep. I want one that will float to hear what is above, similar to the floating wire for picking up radio messages safely.