I replaced the entire power antenna assembly about 6 months ago with the $200 one from FCP. It was installed by a Volvo shop and worked perfectly up until two months ago.

Most of it rises and falls fine. The top tip of it stays "out" the same amount (about 1.5 inches) regardless of whether the antenna is up or down. What can I do to fix this?

 

It should be oiled every now and then. Use WD40 and a rag. Run it up, spray it a little, run up and down a bit, add a little more if needed and wipe up off excess with a rag.