I know this will be of no help.
I’m 5’8″, 31″ inside leg (and older than you 🙁 ).
I have purchased the previous version of the Scandal in Medium, after year’s on an old school 26″.
I have felt that the top tube was slightly too short, but that could be because the bars are so wide to what I was used to, but overall the bike does feels long.
If small and a half is required, then a longer stem and narrower bars may be better as you can make a smaller bike ‘larger’, but impossible to make larger bike ‘smaller’.
( Smaller allows for more technical riding, than the medium, so it will ultimately depend upon what sort of riding you plan to do.
Regarding dropper post, I went for the 150 drop, and still has room to raise or lower.