So last night I went to sleep but all I could think about is how many times I washed out. This morning I began comparing my twin (cartel binding non-channel system) and custom x (cartel with channel system). I use the cartel binding with channel system on both the custom x and sherlock. On this binding, it overhangs my board on heel edge about 1/8 inch. On the twin binding, it is about 1/4 inch away from the edge of the board. Could this cause my issue?
I have pretty much the same set-up. In the interest of eliminating any potential set-up issue you may have with your bindings, here are a few pics from my board (2010 164W CX and L Cartels). I wear size 12 Vans Cirro boots, so the Gas Pedals are fully extended. Bindings are mounted reference width, regular stance, +20º and -12º, mounted 1 increment (1st black stripe back from the centered red stripe) to the heel-side in order for my boots to be centered across the board with equal overhang. I find it has equivalent edge-to-edge response in both directions:
Left (front) binding:
Right (rear) binding:
I also dial in a little forward lean into the highbacks... I find this assists with ensuring I have enough edge angle on my heel side, which keeps me from washing out due to too low of angle on hard heelside maneuvers.
Is there a significant highback angle difference between your two boards? If you used the same riding style on both but had less forward lean in the EST bindings, it may be causing you to have a flatter board during heelside turns, making it easier to wash out...