Help !!!converting single balanced mixer to double balanced

Hi
I have designed a single balanced mixer with Flo=1.8Ghz and Frf=1.9Ghz (CMOS TSMC0.25um technology) I optimized it to give 10dB gain. I used same values (load resistance,width of LO and Rf transistors and DC biases) to construct double balanced mixer but it gave me gain of -3dB. If double balanced mixer is nothing but two single balanced mixers connected in cross coupled manner and there gain equations(CG =2*gm*RL/pi) are same why is this happening? (for simulations of conversion gain I am using PSS
+ PAC analysis ,there is no matching for both the circuits but sources resistance is 0 as I am using vsource instead of port). If I put an inductor to cancel out capacitor at the gate of RF transistor I manage to get 10dB gain for double balanced mixer.Also if I reduce
the LO and Rf frequency say at few MHz i get 10dB gain in double balanced mixer. I am really confused please help.

Thanks in advance