o2 box and speed

First ever post so forgive me if its in the wrong place
ok i am with 02 on prem service. My speed when i joined was great getting up to the max but for some reason its dropped allot
have been in contact with o2 and to be fair they have come back to me but not happy with reply
they say my box is getting into it 16.9mb but when i run a speed test th emax i get is about 13 towards 14

I use a mac and it is wired and only about less then five yards from box to mac

is this the norm to have a high speed going into o2 box and such a low speed going to my mac

sorry for being so stupid but dont understand the reason

any help

I guess the 16.9Mbps is the rate at which your router syncs to the exchange. Because of ADSL and TCP/IP overheads you'd expect to get roughly 85% of that in useful data transmitted, say circa 14Mbps. I don't think you have anything to worry about.