thanks again for input. i've spent a lot of time on this issue and want to offer an observation that may help others. the problem primarily stemmed from positioning the adjustable enlarger setting to the 'correct' position indicated for 2 1/4 x 3 1/4. if i backed off this setting prior to negative placement the uneven light distribution resolved sufficiently if not imperfectly to accommodate my 75mm lens until i purchase a new one. Of course moving the enlargement head farther up did result in the antipated fall off created by the smaller light circumference, but the hot spot and crescent distortion is greatly diminished. i just wanted to offer up the observation that for my particular set up the focal length of the enlarger lens being currently 75mm didnt strictly cause a problem. Your input was awesome so thanks, i've learned a ton about the enlargement process and relationships of the elements I didnt fully appreciate before