The issue should not be with the cut away lifter body but with the material around the roller. You need a roller lifter with the wheel shrouded (like Crane 66550's) so the passage doesn't get exposed.

If the shroud on both the front and back of your lifter is the same then that is likely the issue. The shrouding is usually longer on the back side so the galley doesn't get exposed.

The lifters in your photo don't have enough of a shroud and will expose the galley on a .600 lift cam (had the same issue).