I would figure that the 180º phase difference between the legs would work in favor of tying them together. Perhaps parallel instead of serial...?
I wish I had paid more attention in physics...
--R
Well it's not 2 phase power for a 220v device wired directly across L1 and L2, it sees a single phase voltage. My clothes dryer has just three connections on it's power cord, L1, L2, and a safety ground that carries no current unless there is fault/short condition. So it's just a simple 2 wire 220vac circuit for 220v devices and if you have two CTs measuring the same 2 wire circuit, how can adding their outputs together not give twice the true current flow value? Forget the 120 loads for the moment and just think about simple 220v loads.
From: Split-phase electric power - Wikipedia
A split phase electricity distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential and light commercial (up to about 100 kVA) applications. It is the AC equivalent of the original Edison 3-wire direct current system.
And to complicate it more, I bet you need to rectify and filter the CT's secondary voltage to actually be able to measure it with a standard micro based system, so all phase information if even useful is lost. Oh what evil webs we weave somtimes. 
Lefty