In fact, the experience I mentioned with the 2 hour exposure was not with a condenser enlarger at all; it was a 10x10 Saltzman Chromega, a very even diffusion system.
?? You can see an image of the lamp filament in a diffusion system?
So, if you follow your own advice and remove the lens, then tilt its axis in relation to your eye first wide open, then repeat the same tilt stopped down, the reason for it will be perfectly obvious.