Ah, I think I get it - it's because if I station it off, I get 2.1:1 on the turn (with 50% equity) and 2.2:1 on the river (with 44% equity), so that's why I get the EV's that I do, wheras if I jam the turn (with 41% equity vs his calling range, and 24% fold equity vs. his turn raising range in a 51bb pot when I jam) the odds are worse.

Have I also interpreted CREV correctly in that if the EV of a turn call is ~15bb, and the EV of a river call is ~23bb, that I can say the EV of that line as a whole (ie. making the decision on the turn to call any river) is simply 38bb, or is it somehow more complex than that in some way I haven't thought of?