Back in the early 1990s co-designed a custom tandem for a guy 6'7" with a stoker that's 5'2".
Bullseye made us a set of custom 220mm cranks with a custom Bullseye eliptical cross over chainring for the pilot. Had the front BB on that tandem raised a bit so cranks would clear on corners.
Stoker's crossover chainring was same amount of teeth. Crossover chain did a bit of an up/down dance when they were pedaling but worked out great for both riders.