Just thinking out loud here...
I believe that a PBS cube relies on the actual laser beam being linearly polarised in order to work efficiently. The higher the polarisation ratio of the laser, the more efficient the cube. Do these 445 diodes have good linear polarisation?
Put the waveplate in front of the cube and slowly rotate it, that should give you a clue, as the beam should change from going straight through to coming out at 90 degrees.
Jem
Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.”... Douglas Adams 1952 - 2001