Thanks to all for the many stoker stem threads and contributions. My 5'2" stoker has been complaining for a long time that her arms tire quickly when I ask her to get low on our medium/small CoMo Speedster. And I've been noticing that we pick up a good bit of speed on the flat when she does. I finally cut ~1.5" off the inside bit of our stock CoMo stoker stem and we both just love the difference. She's much more comfortable in all her positions plus we are noticeably faster. She now has a 3 cm drop with her stem slammed.
We kept her relatively narrow cowhorns, even though her hands rub my thighs if she grips the end of the bar. She just doesn't wrap her hand around and likes it fine that way. Narrower is aero-er.
Now I'm thinking about a fixed stem. How do we measure steeply angled stems? From the center of the captain's seatpost at the top of the stem to the center of the bars? I get 125mm for that measure now.