Inventor 2010 iFeature placement

[Enfiel3D]

Greetings!
I started to explore iFeatures not long ago, and now I encountered something I can't explain or find the way around.
I defined my iFeature (a relief groove for the thread) to rest upon two circular edge projections.
But when I try to place this iFeature on the part, I cannot pick the edges to serve as reference lines for my purpose, because Inventor simply does not allow that. I can olny pick faces, which give me completely wrong reference lines. What the matter? I can can pick only the edge when I'm not placing iFeature, but in iFeature mode it is prohibited? Am I doing something wrong?
Please advice!

[dr_fleau]

The way I understand iFeatures is that they are just smart sketches, with some commands attached. Therefore, when you place an iFeature, Inventor wants to place the base sketch somewhere, and that can't be on an edge. Place your sketch on the best face for what you have to do, and check the "Edit sketch immediately" box. You will then be able to constrain the sketch the way you like. The rest should all happen magically. *poof*

Hope this helps.

Pierre