Fringe Control (Yellow/Blue) +light focusing

OK i'm in the process of pulling apart my OHP. The fringe control moves the lamp+condensor assembly up and down, suppoesdly to remove colour halo's - I have found a few sites mentioning that this must be adjusted or the projection lens will get hot

I presume this is because the image converges on smaller point on the lens ?

anyway, I'm only using a 7" tft and I want the light to be focused on the tft only not the entire glass as normally used. to achieve this do I move the condensor or the whole lamp assembly closer to the TFT ?

James