[Let's see....OEI cruise fuel burn 300 Kgs/hr, fuel below the flange 228 kgs.....math is sure not my strong suit but I'm pretty sure that is not 20 mins.].
Sorry, early morning brain fade on the number. The quotation marks were to indicate approximate 139 OEI value but should have been more like "~45 min".
I have confirmed there is no crossed valve of any kind in the 169. It is not necessary and I suspect it could not be certified without boost pumps (can't compare to older designs with different engines and fuel configurations subject to different - some now outdated - certification standards). No offense intended to other types.
Each engine draws fuel from it's on-side tank. Since the tanks are inter-connected like the 139, engine fuel is essentially combined until the flange is reached (collector cell capacity app. 160kgs). This is to assure at least one engine has fuel in case of a tank leak. It's one of the ways to meet twin-engine certification requirement for independent fuel supply. If OEI, the only unusable fuel is on the failed engine side, but only once the flange level is reached.
Not having boost pumps saves cost/weight/etc. The only drawback is that the collector cell fuel unavailable in case of OEI.
Regardless, most of us always want more fuel but if that unavailable fuel is a concern when OEI, I repeat my question: Why, by that time in the flight, would you still be out of range of a place to land. Baring some significant other problem, I just can't figure that out. What am I missing?