You're exactly right, the Bulb Bias parameter is key. It's difficult to describe in words what it's doing, but if you mess around with it you'll hear right away the effect it has. That in combination with proper gain staging is key. It's amazing how much increasing the output levels at each stage (vibe-> drive -> amp) can change the character of the overall effect.
It's been a while since I messed with the vibe parameters, but I remember the Bulb Bias parameter being the key to getting close to the fat univibe tone that all vibe lovers are looking for. At least that's what I found back when I still had a Sweet Sound Mojo Vibe to do a direct comparison. I only bring it up because I have not seen anyone mention that parameter in this thread and I have not downloaded mrstrat's preset yet. There was still something about the Mojo Vibe that added a "creaminess" to the tone that the Fractal Vibe alone could not capture, but that could probably be achieved by other means.
I'll definitely download the preset and give it a spin. Thanks for posting it!