Yes great puzzle and definitely best of the "big 3" this week. Its certainly a way of making sure solvers can fully parse!
Speaking of which, can someone explain parsing of 13 - i know the extra letter, and where it goes, but the parsing i have seems to require an extra letter.
ive also just worked out the 3rd character which was eluding me (and i was about to ask for help) - very sneaky proximal!