I have not tried this so I don't know how well if it would work, but it seems to me to be a rational solution to your problem:
Take an empty case and smear some fine lapping compound on the contact areas of the head. (You can buy lapping compound from Brownells, a gun shop, or an auto supply store). Then manually run the case up and down through the stripper clip to "tune" the contact points of the clip.
I would hold the clip vertically with one end on a workbench and push the cartridge down until it contacts the table and stops. Do not push the cartridge all the way out of the clip. Then turn the clip over and repeat (rotating the cartridge and applying more lapping compound as needed) until the cartridge moves freely, but still with some resistance (you don't want them loose).
The reason I would not push the cartridge all the way out of the clip while lapping is to keep the ends a little tight; this will help ensure that your cartridges stay in the clip until you are ready to charge your rifle.
Finally, thorougly wash out the abrasive residue with soap and a toothbrush, dry, and test with a new cartridge. If still too tight, lap it some more.
Use a new empty case for each clip you tune and be sure to throw the "used" cases away after you're finished. Remember that, as you are gently grinding your clip, you are also grinding the case (this also helps ensure that your finished clip will not be too loose). You do not want to--or allow anyone else to--mistakenly reload this brass as its head dimensions will have changed. In fact, I would recommend that you crush the mouth of the case before using them in this procedure to prevent any confusion.
I think that this procedure will result in a uniformly smooth feed with minimal chance of damaging or overly loosening your clips (that might occur by filing, sanding, or wire brushing). It will also only affect the part of the clip in actual contact with the cartridge so you do not remove any protective finish from other parts of your clips.
If you try this procedure, please post your results. Good luck!