I chose to do 5 pattern repeats before starting the thumb gussets.

Then when I was finishing the thumb, I back-tracked a bit since it was getting a bit long. Once I picked up my stitches, I only knit 7 rows before starting the 5 rows of twisted rib. That put the top of it right below my thumb knuckle.

Ugh to the left mitt! I can’t wind up with 48 stitches after separating the thumb no matter how I do this! Aside from that problem, on the 5th row of the thumb gusset section, if I follow the instructions properly, I would wind up with a yo2 before the final 2 stitches just before the thumb marker. That doesn’t work, as on the 6th row those would both need to be knit, which is impossible to do. If I only work 1 yo in that spot on the 5th row, then in a number of subsequent rows I wind up with only 1 stitch where I need to ssk or k2tog (again, within the few stitches before the left hand pattern picks up before the thumb marker).

After several attempts, I abandoned my attempts at making a left mitt and just made another right mitt. The difference isn’t very noticeable and they look fantastic. :)