Ok John,
You can use strips of carbon weave about 7cm wide. This should give about 25-30mm overlap either side of the fillet. Cut strips a little wider because they will fray when handled. I think we used about 10cm wide strips which were excesive in hindsight.
10mm overlap to fibres is Ok if you are really neat.
Cut the strips on the bias ( ie at ±45° )
Then they don't fray at the edges
easier to stay bent around corners
twice as many fibres across the joints.
Plain weave is stiffer and better than twill which wobbles about and gets a mess / stretchy .
Also do it this way for gunwale joining etc.