Perf experts will no doubt 'tidy up' here, but Vmca is calculated, I believe, on a max of 5 deg bank towards the good engine/s and I seem to recall reduces by around 3kts per deg of bank up to that since not so much of the available rudder is being used to control yaw. It is considered that the loss of lift up to 5 deg is insignificant. Is that too simple? If so, I'm out of here!
