Rockwood is so close that WDFN would still rule over the other 1130s. Reception would be hit-or-miss with one location having a nice signal and another, a house or two away, would not be able to listen to it. Signal quality would change from one day to another as changes in soil moisture change the soil conductivity between the towers in the nine tower array. The array was (still is?) actually plotted to have theoretical total zeros along some radials, but, in reality, that is never achieved. Expect the signal quality in any direction not north of the array as the pattern weakens, any suddenly lousy the Monday morning after the crew does occasional maintenance and gets it back to tight spec (as has recently happened with 950 WWJ).
WDFN even has a major lobe so narrow that it suffers in Downtown Detroit and western suburbs like Canton Township. It is kind of like WDTW was, though not quite so severe. (I wonder what WDFN's NIF level is).
Another thing to note about reception of stations from very close distances in very deep nulls - the "perfect" null may null out the carrier perfectly, but the same nulls will fall on different radials away from the carrier. You may find such a signal unlistenable on an ordinary (diode detection) AM receiver, but strong and clear on a radio with single-sideband capability (e.g., a HF amateur radio transceiver with general coverage tuning into the AM broadcast band).
Another quirk of this is what happens when a deeply directional station is running I-BLOCK. I've been where WXYT 1270 is so well nulled (daytime pattern) that another station on 1270 may be heard clearly in analog, with no interference from WXYT, whilst 1260 and 1250 are wiped out by WXYT's IBOC!