If a small amount of material is removed from this shoulder then cartridge cases are going to be more positively grabbed by the inward-directed claw.
Where the extractor claw rests when there is no cartridge in the chamber is, consequently, irrelevant.
I disagree. When there is a case under the extractor, that shoulder contacts nothing, so there is nothing to retard its inward travel. As MNBud stated, it only comes in contact with the slide when there is no case present.
You can remove the whole shoulder, and it wont have any more inward travel than a factory extractor if a case is present. The more you remove, the more likely youre going to have a feeding issue due to the extractor being improperly positioned in the slide, which is what I believe MNBud was getting at.