So are you aimed right at WLIW? And since you note a discrepancy in locations, are you certain of WLIW's location too? Some coordinates here:
http://en.wikipedia.org/wiki/WLIW
Of course, you can always tweak and check your reception for a stronger signal. But keep in mind that some tuners are just better than others.
Any chance that those other PBS stations could bring you the same content; WNJN & WNJB? You'll have to add a VHF antenna of course.