27% KOH is the best electrolyte to obtain the most Hydroxy by electrolysis.
If you are seeking the best, you know what to reach for.
Yes, you are correct, the smallest plate in the cell is the control plate.
For example, using tubes within tubes.
The smallest diameter tube controls the current.
The other tubes (beyond the area of the smallest tube), are not productive other than by contributing shape and ease of fabrication.
NASA uses 27% KOH.
To me, NASA is the standard.
Whatever concentration you use, measure it and you will then know where you are in relation to NASA.
BoyntonStu