That's curious. My 638, which has recently replaced a 442 (which has the same dimensions) wears a CT 405 grip and a Comp I speed loader works perfectly. If you have the CT 405 grip you shouldn't be having trouble getting a Comp I speed loader lined up properly.
Now the CT 405 grip is very thin - uncomfortably so (for me) after a dozen rounds of defensive ammo. I've thought about switching to the 305 version which appears to be a bit fatter and so might be more comfortable during longer practice sessions, but haven't made the move yet. What I don't know is whether the edge of the speed loader cutout on the 305 is any thicker than on the 405. If you have the 305 grip and it actually is thicker around the latch area, then I can understand why you are having speed loader problems, and I don't think there will be a solution (other than the speed strips.)
That said, my daily carry setup includes only a single speed strip in a belt holder. As you have no doubt discovered, speed strips aren't nearly as fast as a speed loader, and require some fine motor skills which they say will disappear under extreme stress. Still, I haven't found a way to carry a speed loader discreetly with the clothes I normally wear.
