I think getting it right for the stoker is harder than for the pilot. We don't have an infinite range of bar height, and we're more limited in relation to the cranks, even if the frame size is theoretically right.
I think generally I'm quite forgiving of bike position, I've ridden 200k+ on (counts) 3 different geared bikes, 3 different tandems and 2 different fixed bikes. None of my bikes have the same seat height or saddle/bars differential and I get away with it. I'd love to be able to claim this is because I have a strong core but I think I'm just lucky.
The Swallow was great for me, almost straight away, and the Longstaff matches that, except that I lose space between me & Chris. keeff & Sue's Thorn has lower bars (I don't really understand how, when surely Chris's saddle is the same height) but apart from the numb hands kicking in sooner, it was fine.
Feline- our tandem has a telescopic stem, have you tried one of those?
I have short legs and long arms so maybe I'm just a more tandem-standard shape? I thought from WSD sales pitches that this was unusual for ladies, maybe tandem frames are actually more like two mens frames than a male + female sizing.
I have a much more upright position on the tandem than my solos, and ride much more on the tops (I don't have any hoods) and don't try and match exactly my solo position. There's no need/benefit. I don't think it's possible, anyway, as we couldn't match the saddle/cranks angle/distance, I don't think.