Recently, when I got my lining checked about a week before the donor's egg retrieval, my lining was 13.5. I thought this seemed overly thick, since we were still a week or two away from the transfer, but was reassured by the technician that it was good and within the range they were looking for.
Unfortunately, I didn't get to see that cycle through, due to a low number of eggs retrieved, so I don't know how that lining story would have ended. But my doc wasn't concerned and didn't adjust my meds after seeing the 13.5.
FYI. Good luck!