IF you don't have any oil around the front cylinder base and the leak is localized around the filter, it is probably one of three things - First it may be nothing more than oil spilled during the filter change that is just now working its way down and starting to drip. It is almost impossible to change the filter and not get some oil spillage.
Second, the oil filter gasket is leaking (making it tighter may only make the problem worse) - Or the oil filter bracket is leaking (This is me hoping that your cases aren't cracked or leaking).
I would try the cheap fix first and change the oil filter. The filter may have visual signs leakage (gasket creased, flat spot, cracked or wrinkled). After changing the filter I always spray brake cleaner all around the area to clean away any spilled oil.
If you still have the leak after changing the filter, you should replace the oil filter mount "O" rings (HD # 11293, two required). Inspect the mount for cracks or warping and if it needs to be replaced you will need HD # 26261 (black) (includes "O" rings) or HD # 26274 if your motor is silver. Or you might want to use this opportunity to do a little chrome and add HD # 26321-99A Chrome Oil Filter Bracket ($69.95 retail).
Hope this at least gives you a place to start looking.