So, as the question states... What is the "right" way to do this?
Purple are the joists. Orange are the edges of the board. Red is the butt joint. Cyan are the screws - mainly doing edge screws
"A" - Just meet on the joist. One screw per side (so, not that dissimilar to an ipe clip)
"B" - Double Stretcher
"C" - something else?
I'm thinking that top screwing with plugs and a 45 degree cut is the correct response. If I just cut at 45 degrees and edge screw, I get the following problem - These screws are too close to the edge to bite into the joist.
So, they will just require some through-screws, with plugs to hide.