Y- Harness Charging

I'm running my sig 1/4 scale cub on two 6s1p 2300 mah a123 packs on a Y harness.
I've been charging the packs individually with my Hyperion EOS 0610inet charger which sees the pack as 5 cells, but when I switch it to 6 cells it charges at 10 amps for 15 min. and the packs barely get warm to the touch!
The question is... since there are 6s2p packs available, can I charge both packs at once thru the Y harness without risking damage to the packs?

I packed my a123 as 6s1p with balancing taps.
On my Big Lift II they are coupled by four as 12s2p, including balancing taps.
At the field they are loaded in the plane with a MasTech HY5020E power unit without balancing, in 15 min.
At home they are loaded with a Robbe charger with balancer.
It works without problem!