Yep, my neck is shorter than average. I know, because even *petite* turtlenecks have too much material for me! Every now and then I will find the rare turtleneck that works - that isn't a mock (hate those) but a true t-neck that leaves a pinch of room between the top of it and my chin, instead of trying to swallow my chin. It's not my best look for sure, but sometimes you want a warm neck and flattery is secondary.
I look silly with a popped collar. I don't think short vs long necklaces make a difference. There is, however, a big challenge finding dangly earrings: many of them will brush my shoulders!!! My DD16 has a graceful, elegant long neck and she looks amazing in these super-long dangly earrings.
You know, I always thought I had a weak chin, but my DH this past week told me my chin is just fine - it's "average" - it's my neck that's too short. LOL.