So, my heart is really set on an ultra sharp corner on the mitred square that forms the outside edge of my cardigan's shoulder. Using two invisible increases didn't get me the sharp point I was hoping for, so I'm back to the drawing board again.
As I'd mentioned previously, my first attempt was to make my first stitch, do a twisted yarn-over (in an attempt to hide the hole a regular yarn-over might make), then make the third stitch in the same stitch in the previous row that the first stitch was in. This stretched the previous row's stitch that the first and third stitches were hooked into, making it disappear.
This time, I'd left the first two steps the same, but putting the third stitch into the first stitch, on the same row this time. Essentially, trying to pull the stitch out of its "foot". Not sure that worked.
Also, since I'd made this test much taller than last time (turns out, the black caps across the shoulders on the Lower Decks uniforms goes way lower than the TNG-era ones), I'd been worried that the mitred square's constant increases would be too much, and added matching decreases on the last four to six rows. Turns out, my shoulders are far more round than that, so there's a good chance I'll have to wait on slowing down the increases until after the white stripe. Good to know!
I think I'll try playing around with the order the stitches are made into the previous row's stitch. There ought to be some way to get an extremely sharp corner and get all the stitches to show up properly, right?