I would have quite happily murdered a box of kittens for your seat at the end of a long ride.with a very low, extra-large seat
https://www.cyclechat.net/forums/recumbents-trikes-and-hpvs.11/ or @mrandmrspoves might make a better guess. On DF bikes, I pull it tightish on biggest-biggest and then add a link, which sounds to me like it might still make sense.
If he is, he's kept it quiet. Lol.
And I know nothing about hand bikes