Hi,
I too think this is a great layout with a complimentary selection of plants. I wish I could grow them this well!
One thing I do feel it is missing is some height in planting to balance the upright wood. You have suggested before a contrasting coloured stem plant at the rear and I think this would finish the scape off perfectly 🙂 Also like Ian said, keep the hydrocotle trimmed, maybe enough to expose the highest tip of the left underlying rock which will balance the hardscape better IMO 🙂
.....oh, and i think it's always worth entering the IAPLC, if you don't youll never have a personal benchmark to work from and try to improve on 😉
Cheerio,
Ady