I agree, reading material for rivers like ours is extremely hard to come by. There was a great article in Musky Hunter several years ago documenting musky behavior in small to medium sized rivers. (The article was mostly about the rivers in WV which is where the study was done.). It was the single most important article relating to ‘my river’ here in this section of the Allegheny.

Yes, they will be in 5 ft. or less water at times and especially late at night/early morning when the temps spike during summer. Be sure to get in and around those big rocks that you mentioned. If the water is clear with less than 3mph current, they could be suspended in that 20ft. area.