Got back from HAI Sunday night. Great show!
The sponsons produce no lift at all, just drag. In fact, the hover performance is probably about 1% the poorer for the vertical drag on them - 200 to 250 pounds.
If you recall the Sikorsky Shadow (S76 with the long nose and extra cockpit) it lost 150 pounds of hover performance due to the extra length caught in the rotor downwash.
For the 92, putting the gas in there was a conscious decision, no gas in the belly, which is the first thing to hit the ground. the sponsons are lined with a crashworthy bladder and no fuel spills when the whole shebang is dropped from over 50 feet with full tanks onto concrete.