Perhaps the engineers aboard here can verify this suspicion of mine .....
The thought is that when WHLI raised their power to 10,000 watts, they went to one of those casual two-tower directional signal limitations NOT as much to protect the full-time Cleveland omni-directional WTAM but the daytime station BETWEEN WHLI and WTAM. That's the wee WGPA Allentown-Bethlehem.
After all, WHLI traditionally has been a strict daytime-only station for decades. WHLI, WGPA and WTAM are pretty darned co-linear. So a new, beefed up 10,000 watt WHLI pulling in their *daytime* signal away from Cleveland also would be protecting the Allentown station.
Two-tower AM arrays effectively maintain a more gentlemanly null that those more severe signals radiated by three or more towers.
Cleveland is over 400 miles west of WHLI's signal when WHLI is on the air in the daytime. I'm just asking if WHLI's casual, relaxed null in that west direction is primarily to protect the closer WGPA.