Ted's suggestions runs in line with mine. I don't own any SY Kydex and I would not want to urge you to do something you are not comfortable with, but if I was going to fix this myself, then I would try to figure out where it's tight/binding.
If it's tight on the blade itself as opposed to the mouth of the where the tension is set on most of the sheaths I do then do then I would suggest the following: Note, you can tell if the sheath is binding on the blade by excessive smoothing of the coating on the blade. This is subjective I know but, you should be able to hear/feel/see where the drag is when you pull the knife out.
1. Remove the nuts and screws (all of the metal) from the sheath which should not be a problem with the design not using rivets.
2. Put a layer of blue painters tape or masking type tape on the length of the blade on both sides.
3. Get a hair dryer or heat gun (on low) and move the hair dryer across the length of the sheath on both sides for a couple of minutes (if you use a heat gun then try 1 minute seconds per side on low) and then put the knife back in the sheath and let it cool for 15 minutes. Avoid heathing the mouth of the sheath (tape if up with a few layers or just don't heat it) if it's just too tight around the blade.
4. If this was not enough to loosen it up to your liking then repeat step 3 and increase the length of time you keep uniform heat on the Kydex by 1 minute. Repeat this process until you find a fit you like.
Error on the side of not heating up the sheath enough becaues it you expand the Kydex too much, then that is a whole differnt issue that's tougher to explain.
If the issue is tension at the mouth of the sheath (by the handle), then I would suggest the following:
1. No need to tape the blade.
2. Remove the nuts and screws (all of the metal) from the sheath which should not be a problem with the design not using rivets.
3. Get some gloves of some kind.
4. Heat up just the mouth of the sheath using the times above (erroring on the side of too little heat).
5. Insert the knife and use your gloved hand to put light pressure on the mouth of the sheath to form the Kydex around the handle.
6. Keep pressure on the mouth for 5 minutes and let everything cool in your hands.
7. Let the whole thing cool for another 10 minutes.
8. Repeat from step 4 if it's not to your liking.
Good luck man.
