WJFP is indeed the reason for that southwest protection. As 'WVCH', religious for decades, they were also a 1000-watt omni at the time WGSM was 1000 and omni.
As a DXing kid, cheaply provincial as I was, I smugly thought that all those weaker stations that weren't from the extremely populated and elite 'home' of NYC and Long Island were -- how to put it -- second citizens?
After having matured somewhat over the years (but still a DXer) I learned that 50,000 watt 'WQXR' from NYC and 10,000 watt WHLI used directional patterns in the daytime to steer clear of two Pennsylvania stations of lower power that already had established their signal area before WQXR and WHLI wanted more wattage. 1010 WINS needed to pull in and 'watch it' to avoid their newly-approved daytime 50,000 watt signal from spilling onto 1010's in Baltimore and Norfolk VA and those FCC-authorized signals.
Someone here will know if the distance between the physical tower sites or of the 'downtown' spot of the cities of license is the more crucial factor in any decision. I'd guess 'tower' coordinates, but what do I know, lol?
WNYH's southwest null is very vivid in the day along a stretch of the SOB Expressway's northern lanes. Wicked sounding audio. I'd venture that, being 25,000 or even 20,000 watts the slightest tilt of WNYH juice sent to the meters of any of those sticks could send a lot more interference at Chester PA than their old WGSM's 1000 watt omni ever would.