What if it used other geometric shapes, like a triangle e.g.? Or maybe even different shapes for the "attacker" and the "defender"? Like a triangle elephant pushing a rectangular elephant, the later would turn out of the way faster?
Regarding "construction of 100-traders long "lines" of caravans", "just looks bad": totally agree, and have proposed solutions a couple of times.
Regarding "markets now generate income at a fixed rate": I was thinking about it to emulate "local trade".
The "logarithmic" idea is interesting, quite different from what I was in principle thinking for a new system, while I don't agree much with "garrison workers in your markets to leverage full efficiency", it seems a waste of units.