I have a 10m E5 & really like the pivot setting on 20m lines.
Underpowered, what winds /board /weight ?
My thinking is that what power you gain on 23,s you loose on speed through the window - so I have been on 20m lines for as long as I can remember, I only ride surfboards.
Great kites, waiting for them to go on sale to get an 8m.