Mid sound spots are not really a secret,
Eatons Neck triangle, outside Nissequogue, Stony Brook Harbor entrance, the area from Flax Pond to Port Jeff Harbor including Old Field Point, then the Can 11 ( Mt.Misery Shoal ) area can be great at times. Can 9 at Rocky Point, 7 at Shoreham, all the cans are near the drop off ( naturally) and there is usually good bass, bluefish, and fluke fishing in those areas. If you look at a chart of the sound and fish off of any of the points or the harbors, you are going to get some decent action most of the time.
I forgot to mention Smithtown Bay, some good spots there. There is a chart around that shows all of the wrecks and shoals, I found it for sale on the web but I am sure it is available in many tackle shops.
Middle Grounds ( Stratford Shoals ) has some very productive spots on all sides.