So the print (half, since the DP2 isn't large enough to print the whole thing in one go) failed, but though that rolercoaster I was able to get enough of a print to see where my fingers lined up.

Slightly suprisingly... I actually only had to do a few small tweaks here and there, most notably that Finger3 and 4 are 4mm closer together. It seems I've finally had enough ergonomics experience to know what layouts can and can't work.

The length is also 2mm shorter, and I've also reduced the size of the "Tetent" text. 

[19 Mar] I've been thinking all day for a way to make the first person perspective look nicer, and I've come to this simple yet somewhat inescapable solution:

I've added 1mm thick walls to hide the Tetrinsic cutout. I wasn't expecing such a strategy to make the perspective look as calming / non-distracting as it does. 

I'm also considering adding a cutout to the sides (brown = skin, purple = sides of device): 

This idea comes from the book I was using, where the front and back hardcovers were slightly further forwards than the paper inbetween. The book feels more comfortable and grippier than the flat-walled print. I've modelled it in below: