Projector mounting location to reduce noise
Just as a frame of reference, 26dB is about the sound level of a person breathing. Typically these are measured at a distance of a meter from the source. Whether or not this will be objectionable is mainly a question of personal preference (and how much other sound sources such as your speakers mask it). My suggestion would be to pick up a computer case fan with a comparable decibel rating, put it where the projector will go and see if it would be a problem for you.

As far as increasing distance goes, it will obviously help. Sound level drops by roughly 6dB for every doubling of the distance, so at 2 meters it should be barely perceptible and at 4 meters you would have to try really hard to pick it out.

Bear in mind that 26dB is the claimed decibel rating, and the actual noise level you perceive can vary depending on frequency, vibrations in whatever it's attached to, etc.