[Chimera-users] odd output from surfnet

I'm trying to get an image of channels in the attached protein. It's actually a dimer, & the surfaces looked bizarre for the dimer, so I thought maybe surfnet was choking on the repeated residue numbers when you use chain ID, so I clipped it down to the monomer. That' still odd. I've attached a png of the result, using the defaults, & the pdb file of the monomer. What am I doing wrong? Is there a way to get the n largest channels, instead of all of them? Thanks! Irene Newhouse