So here's the image I posted earlier.
A twingle set-up of 7" fins, spaced 2" off center, foiled inside, flat outside. Water flow along a plane halfway down the fins, so 3.5"under the board, at 3 m/s and 15 degrees AoA.
Quick note on the colors. The colors represent the velocity, so if you look at the right side of the images you see the unpertubed flow in green (3 m/s). Going to yellow, orange and red the flow is accelerated, going toward light blue and deep blue the flow is slowed. So the red-orange areas represent lift (accelerated flow, less pressure), while deep blue is flow that is almost still or even turning around as you can see in the turbulent stalled region.
I need to process the other images to make them lighter, tomorrow. Mandatory disclaimer, these are fast simulations, they give an approximate idea of what's going on, reality is more complex.
Bonus Image, same situation at 20 degrees AoA. The wake is more turbulent and the pair generates less lift than at 15 degrees but remarkably the flow is still mostly attached on the outside fin.