Problem with Autodesk I-Mates

I have been using Autodesk Inventor’s vex parts and tried to extend a C-channel but the I-inserts(or I-mates) didn’t extend with it. I tried manually adding the I-inserts, but I couldn’t get them to be consistent with the other I-inserts on other parts. Is there a good way of creating the I-inserts so that they will always be lined up correctly?

Here is a video that explains how to add iMates:

The method I use is very similar.

Thank you so much! That was extremely helpful!