I had the problem that my belt looked very weird and did not mirror properly.
After deleting it and making a new one I found out what the problem was.
The Belt was not centered properly like my orc was so while the shrink wrap and the snap forced it to be on my orcs waist the mirror was simply not able to make the shape fit the orc everywhere.
If your Belt does not fit perfectly try going into object mode and just scale it up a lot, if your belt becomes really big on one side while staying significantly smaller on the other then your center is off.