I didn't torque those two bolts. They are actually smaller bolts and came out easy so when I reinstalled, I tightened as hard as could. When I install my Stern subframe brace, I plan on checking to see if they are still tight. I did re-use them as ECS only supplied the 4 subframe bolts. Don't take my word for it, the 2 smaller bolts are support bolts so I don't think they are stretch bolts.
If you don't remove those 2 bolts, you will not get the gap needed towards the front of the subframe. That was the issue I had initially. Once I removed them, I was able to get the clearance needed to insert the collars. Make sure you loosen all 4 other bolts, but don't remove them. I posted a video on youtube that might help you locate the bolts easier hopefully.
MK7.5 GTI Rear Subframe - YouTube