Just musing over the issues here it seems that the large bore balance pipe between tanks is not a problem. Rather more that tank breathers and associated carbon filters and rollover valve restrict balancing between tanks and cause over pressuring to engine.
I shall leave the filler cap open for a while after fueling. Most of the instances of fuel mist on the windshield that I've experienced have been immediately after refueling. This is in line with Richard Wood's comment about vent restrictions. Thanks for the insight.
The fuel leak situation was due to my using screw-type (not worm screw) hose clamps on the injector hose barb without thread locker on the threads. I feel better now that there's a plausible theory for the puzzling coincidence of leaking with gassing up.
