No good ideas, but having the same issue.  In trying 800 MHz and 900MHz each separately for about 24 hours, I received even lower hash rates on CM.

I'm running 20 Gridseeds, RaPi, and CGMiner 3.7.2 showing ~7.2Mh/s on miner, but only showing up ~5.0Mh/s on CM.  That puts each GS averaging about 250 Kh/s on CM, but showing 360 Kh/s on CGMiner.  My GS have fairly equal accepted work, are mining pretty efficiently at 850 MHz, with minimal (0-3) HW errors per unit per 24 hours.  Reject rate is just over 1%.

I'd too would like comments back if others are experiencing lower hash rates on CM and any tweeks or adjustments to increase real, recognized hash rates on CM.  Hey - not complaining though - with the recent ~200% returns, it was like getting real 500 KH/s from each GS! 

Thanks for a great pool and the professional efforts/information from everyone!