Richard,
I feel your pain, I went through similar pains.
I'm no C# expert, however, can you do two things to help troubleshoot? In your C# code, add a debugging line that will dump all of the POST data as it hits your C# code for review. This ensures your C# code is receiving all the form data. Part two, can you temporarily run your server through a proxy like burpsuite or similar to see exactly what is getting posted to Click Dimensions (You'll need to have the C# ignore SSL Warnings).
It would also be helpful to see a screenshot of your FormCapture settings.