Ah, no. The Input Keys and Tangents are unrelated. The input keys just have to be set to match the integer index of the spline point to get useful results. My tangent calculations are just because I have a polyline (points only) that I’m trying to make a smooth path from. In my case I’m calculating the tangents by finding the vector between adjacent points, and then scaling it to the length of that segment. (Normally I’d scale by 1/3 of the length, but Unreal wants tangents 3x longer than traditional Bézier math calls for.)
For completeness, here’s that function (with edge case tests to handle the first and last points specially):
