When I run one of my L3's it shows a pretty steady hashrate of ~520 which is pretty close to the stats page on the miner.  However, if I add another one of my L3's, both rates drop and fluctuate from ~450 to ~480 each.

Unit 1 shows ~520
Unit 2 shows ~510
Unit 1 plus unit 2 shows ~950

I'm getting ready to add a third into the mix to see what happens.  But, is there something I should be doing?