I have a shape that i want to add a surface element to. It's a rounded surface wicht I want to add a fading sharp edge to.

I linked a sketch and the edge I want to add and my model below.

The edge fades out fairly quickly towards the bottom fillet and fades out slowly towards the top (can be a but further up than in the sketch). On the white model it's the bottom edge I want to use, just straight instead of curved up.

I have no idea how to do it, I tried with a 3D sketch and then boundary surface but I just can't do it.

Please help!