Yeah, you are getting a thicker sound because the signal is being doubled; it's like an analog chorus except without the swooshing sound. I would also bet that the clean signal is partly out of phase with the loop signal, but (because of the multiple gain stages and EQ) not exactly out of phase, and that's a good thing. It means more fatness, less signal cancellation.
The business about the levels being too high/too low in the loop is something to be aware of as a general possibility, but as you have found, it's not always the case. Experimentation is key.