New fibre - a lot slower than the estimated speed

[#1]

Hi all,
I had my upgrade to FTTC yesterday, all went well and it's working fine
I have a query about my speed - I'm currently connected at about 20Mb, when the engineer tested with his meter he was getting about 22Mb and he said that was pretty good considering the distance to my cabinet, which showed as approximately 1.1km.
When I was ordering fibre the estimate I was given was approx 37Mb, and in control panel/high speed broadband it says I'm currently on 37Mb (see attached).
I'm just wondering why there is such a big difference between the estimate and what I am currently getting. Is it because it's still early days - will the speed pick up eventually? Or am I just limited by the length of cable to the cabinet? Or is there something somewhere that can be tweaked to give it a boost?
I'd appreciate your feedback.
Thanks!

[#2]

Hi Fru,
The estimates that are provided are based on the length of the cabling between the Fibre Cabinet and your Distribution Point (Telephone Pole). What isn't taken into consideration, is the quality of the cabling, that's one of the reasons that speeds can vary so much.
I find that http://www.increasebroadbandspeed.co.uk/2013/chart-bt-fttc-vdsl2-speed-against-distance is pretty handy as it gives you a fairly good representation of what speeds you should expect.