To be honest I would have thought it works the other way around. In other words less sun=more tightly packed with more sun=wider-spaced culms. A sunnier position for a Phyllostachys usually results in more wandering. My Spectabilis started out in a fairly sunny position with morning thru afternoon sun in 2003, but as they've grown the canopy of culms and blades have shielded the ground so that it only receives a little morning sun. I presume this has limited the wandering. My two plants are planted near a boundary fence and each autumn I've driven a spade around the stands to limit growth further.Noticed that your Spectabilis (the same plant you have used with your forum posts?) has shoots that are extremely tight. My Spectabilis only gets early day sun which moves behind the house at about 2 o'clock. I'm guessing that's why the shoots are about 7 inches apart, in contrast to the plant in your picture. I'm guessing your plant gets all day sun ...
Thanks again for the kind commments re the garden.