Hi Gregor, you'll probably want to make the top profile of the heel to come from the edges of the sole so that you know that the sweep will come right up and touch the sole.

You can do that by selecting some of the edges from the sole and then use Ctrl+C and Ctrl+V (copy/paste) to duplicate them as separate curves, then you'll know that something built to that come right up to the sole surface as you want it.

Then it sounds like your remaining problem is capping the top area of the heel? Sweep will only automatically cap ends that are planar. In your case here your top curve won't be planar so it won't be automaticaly capped but you can use the same curves you used as the top profile for the sweep as a cutting object in the Edit > Trim command to cut the sole surface, then that trimmed sole surface will become the cap for the sweep. Use Edit > Join to glue it on to the end of the sweep after you have trimmed it.

Let me know if that does not make sense.

- Michael