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Consider IN+ → OUT- path. You can see that source of M5 is a summing point of two signal currents - main one from the MA1 transconductor and reused one from MB2, mirrored by MB3-MA3 current mirror. So, the total transconductance is Gm=gm_MA1+K·gm_MB2. The advantage of RFC over FC is as following.
Suppose the same current consumption and DC OPs - the gm of every device is then easily scaled with current.
The FC has M1 input device biased with 3·Ib and M3 with 4·Ib (total current is 8·Ib). The transconductance is equal to 3·gm (gm is a transconductance of mosfet biased with current Ib).