The
wiring idea will not be any measurable improvement over connecting the main leads to the nearest convenient mechanical point. While battery voltages (and current) may be marginally different during cranking loads, as soon as the load is removed the batteries are equalized by battery to battery current in less than a second so the total conribution from each battery averages out in proportion to their capacity.
If you wanted to pick the "best" point to connect it would be midway along each parallel chain so the current on average passes through 1/2 the number of battery jumpers and connections.