I mean have the high side 21s look just halfway into the transformer with the high side bushing and coil impedance, and the low side 21s looking back into the secondary side. With that many 21s, my thinking is not to look through the XF.SEL487E providing differential and 50/51- soon SEL 311C or 421 for the step distance.
This comes from an overhaul of electromechanical relaying.
When you say look into you mean into the bus or through the transformer and the respected other side bus? That part is what I'm debating.
without pages of calculations, my gut tells me the admittance values will overlap on one or more and you may have nuisance tripping, especially during energizing