I have had a heck of a time with FC and SEF URLs. For the most part I am not using them. FC uses a lot of Ajax calls and SEF URLs are not working well for these and I haven't benen able to figure out why.
But since this URL is a redirect you could try inserting an SEF url in there, not sure what would happen. If you can open the form directly on the front end you can get the SEF URL and give ti a try.