Having spent six years at KFBK and coming up on two at KXJZ, I have to say that's not right.
Those may be where a chunk of core listeners for the stations live currently, but KFBK throws a solid signal (AM, FM or both in some instances) into the urban/surburban areas.
KXJZ's Sacramento signal overlaps its Tahoe/Reno signal (KKTO), and its Stockton/Modesto (KUOP) signal to provide true regional coverage of the Southern Sacramento Valley, the Northern San Joaquin Valley and the Sierra. And then there's KQNC in Quincy, which doesn't overlap, but the gap between it and the KKTO coverage area is small and sparsely populated.
Neither 'BK nor we are "meant for" a particular part of our coverage areas.