Upstream rate has dropped

[Terryphi]

When I  upgraded to FTTC in 2015 I enjoyed download speeds of over 36mbps and upload speeds of over 7mbps. As I was one of the first connections to the cabinet  I expected performance to drop slightly over time. Download speed has stayed steady at around 36mbps but upload speed has gradually dropped to the current rate of just over 4mbps.
Checking my router stats it shows this:
B0 Line Rate - Upstream (Kbps)   4729
B0 Line Rate - Downstream (Kbps)   40000

Is this compatible with the 40/10 service I am supposed to be getting?

[Terryphi]

Having done some research I find that current upload speed is what is expected on the line length. My download speed is very good considering I am 1.2km from the cabinet.