I am 6 off but I agree that's a sweet Arwen.
From being far off I gradually cut down steps and that's a fun process, but I don't have any more idea now. Will be back later.
For me the most challenging part is to find out the correct blocks for the holes. Once I figured it out, the solution came soon. The pipelining in this one is quite intuitive to me.
Really great aha moment for this one! The way to approach this correctly is the last thing that I would have considered.
I was stuck in a brilliant 2 off the day before, this made me appreciate again the vast amount of serious effort that was put into the level series. 7th DEM done.