AM 53 is fine to me as long as i stay in the western part of it. But u wont find many lonely merchants there its convoy/taskforce property. With patience u will spot even unescorted convoys there. Personally i prefer AM 51/52 which are out of range of fighters. Lots of convoy to herass there.
Its weird that ure tc didnt jumped to 8 it happens generally to me and i still have a minute or more without ships sighted or plane spotted reports. Did u make the changes regarding tc settings in sh3com adviced in the NYGM manual ? 3D tc = max tc.
Just discovered the way to get a fix on the location of the object which cause the jump to tc 8 without getting a contact via hydro or visual. Go to mapview and move the mousepointer around ure sublocation upto a 50km range. If it moves over this object (sub/ship/plane) a lightgrey circle pops up with a time stamp and the general course enough info to close in to it for further inspection.