Upload Speed Question?

[#1]

Hi
So since activation my line has synced at 19999kbps with the HG612 reporting 23000+kbps potential sync rate... either way I cannot achieve any speed test's higher than around 17-18mbps and in recent weeks it seems to have reduced to around 15mbps..
Any ideas why this is happening, I have tried many things to try and improve the connection (inc. direct to modem connection).
Regards.

[#2]

My us synch has always been 20 but I've never achieved more than 15 according to the BTW speed checker. Interestingly speedtest.net reckons I get about 18.

[#3]

Because of various overheads, you won't get real upload speeds much above 18.7Mbps.  For that you need an unlocked HG612 with QoS turned off.  WIthout, max upload is around 17Mbps.
Speedtest sites vary a lot in upload figures;  Thinkbroadband is one of the most reliable for upload speeds (http://www.thinkbroadband.com/speedtest.html). 18.41 avg, 18.68 burst for me right now.  Ookla gives me 18.92.
When I was on SquirrelSave I got a real 18.7Mbps pretty consistently. Dropbox,  Google Drive and OneDrive never seem to manage consistent full upload speed.

[#4]

Hi Thanks for the inofrmation, I think the QOS on the HG612 is probably the reason I'm not seeing what I expect.. I'm aware of the overheads in speeds which is why my sync speed should really be set over 20000kbps to achieve the full speeds but it is what it is...
I'm currently trying to get an issue with latency fixed though I think their may be a fault locally or resets of my modem to avoid Plusnet Gateway issues might have triggered DLM (If it still exists) so might need to get line reset.
I've lost about 3-4mbps of my downstream speed and also lost around 5-7mbps off my upload...