try this off the top of my head turn one of your spots into a volume visible... infinite then go to ranged (click it) and set it for just a guessing at your scale about 100 or 200... if it shows up in your render and the scale is good then play with the lights edge softness... keeping in mind, this will also shorten (view aperant) your light, so you might have to increase the range some... i think though, in this case, i would use a surface visible spot light instead of a volume one... i only say that because if your not trying to take advantage of the 'volume' effect (that is to say, to break the volume and cast shadows within the light) then a surface visible might be best and easier to render... again just off the top of my head... good luck!