Crab
Imagine a 'H' shape with the tanks at the bottom of each leg and the fuel valve on the top of each leg. After each fuel valve will be the engine driven pumps sucking the fuel.
The crossed line is the horizontal part of the 'H" with the valve in the middle. That bit would be the same as the 139 but whereas we have booster pumps the 169 doesn't.
With the crossfeed valve closed each engine sucks from it's own tank - no problem. If you lose an engine then the fuel will be consumed by the remaining engine until the tank splits into two at the the 200L/200L mark. The live engine suction pump cannot then access the other tank so 200L is unavailable. Open the crossfeed and the engine driven pump should (I don't know for sure) have enough puff to suck from both tanks. My intuition tells me that there will be an uneven rate of pick-up that favours the live engine's tank due to a small pressure drop across the crossfeed line and valve. You would have to close the crossfeed as the live engine's tank approach the minimum in order to avoid sucking air.
There would be an unknown and possibly variable amount that remains inaccessible. That's why I favour the low level connector between the two tanks as there would be much less unusable fuel at the end of the day. A valve controlled by a guarded and (tell-tale) wire-locked switch in the cockpit would do the job. We had such an arrangement in the S61N and some S76B's.
The 169 tank(s) are similar in layout to the 139/189 in true 'family' style.
G.