I filed off the top tier on both sides, and had no problems, but I just left them on the knife while I did it.
Point being, if you are just thinking of filing off the top tier, you should have no problems.
After doing this to mine, I have had zero problems with the thumbstud catching on my pocket and partially opening..
Again, point being that filing off only the top tier solves the problem of the partial opening during the draw..
I'm just bored and looking around for threads to post in, but the information is relevant...