I just started using 8 x 10 and shot my first few sheets of film. I made some contact prints and am having significant light falloff around the edges of the prints. My enlarger is a Beseler with a Zone VI VC head. I have the enlarger head up high enough so that the light circle is well outside the contact print frame area.
All cold lights dim at the edges.
You could measure the falloff with a meter to see how significant a fallout you are experiencing. I have seen photographers replace the cold light discs, use pieces of gray cards and other such devoces to even out the light output. If you use a large format enlarger you may be experiencing a light problem. Do like Edward Weston and use a light bulb. It worked for him and it works for me.