Hi Colin
At the risk of trying to teach your grandmother, I also tend to look at the distance to the middle of the top clamp bolt so if that is 30mm or so I would consider using it.
I have a bbb thingy, I also have a Delta Stem Raiser.
There is also an Azonic Hammer with an over all stack of 31.5mm. reach approx 40mm
I also have a spank spike with a single clamp and I believe the lowest stack of all at 26mm but suitable for over sizes bars only but could obviously be shimmed. This is in use at the moment but could be available if I can source an alternative. reach approx 40mm