I have the same problem with the neck. I've gotten to the point where the results are acceptable doing things like David suggests. But I'm a perfectionist and it still doesn't cut it. I don't know if it ever will. My neck is just too sensitive to tolerate a lot of passes with the pressure needed for a str8.

I touch up with what I call a Featherjector. It's an injector razor fitted with a cutoff Feather str8 blade. It has extreme maneuverability and cuts with the weight of the razor only. I can float over trouble spots any number of times to get as close as I want on a touch up. It works.

I don't know if anyone can shave so close with a str8 that you feel no stubble at all even on the tough spots on the chin and neck. if anyone can I'd like to know, and if you have sensitive skin how do you do enough passes?