I appreciate the challenge of using fenced rabbit planes, referencing off the show face but also having to plane against the grain. My preference is to use the fence rabbit, or even a marking gauge simply to establish the position of the tongue and then plane the remaining part of the shoulder with an unfenced rabbit plane you can work in either direction.

Alternatively a matched set of T&G planes is super helpful for establishing consistent dimensions, which can then be cleaned out to full depth with unfenced rabbit plants.

Your mileage may vary, cheers, Mike