I get the impression that they apply a tier-type throttling like satellite based providers, where data is initially delivered at full speed, but once a certain threshold is reached in a rolling interval (e.g. 1 hour), the connection is throttled.
The next time your connection is at full speed, you could try capturing a graph of the throttling as follows:
Go into the 'Download Test' tab above.
If it says "Testing Global Multithread", click 'Classic Linear'.
Ensure the 'Testing' server is nearby, otherwise click 'Servers', pick the nearest and go back into the 'Download Test' tab.
For the 'Manual Test' drop-down, pick a fairly large size that you know will lead to throttling, e.g. '50MB'.
Don't do anything online during the test and leave it to finish, e.g. start the test just before dinner.
At the end of the test, you should see a graph like the following:
If the line is fairly flat for a portion of the graph, then plummets to a much lower level for the rest of the test, then the culprit is most likely your ISP throttling after a certain amount of data is transferred over an hour or some other short interval.
On the other hand, if the level remains fairly low or fluctuates all over the place throughout the graph, then it is most likely contention, such as your Wireless ISP being over-subscribed. In this case, repeat the test early in the morning to see how it compares. If the throughput is much better in the morning, then it's very likely you are connected to an over-subscribed tower.
I'm at my wits end. I live in the country and I am on a wireless internet service provider. We have a receiver on the roof that points to their tower etc. We are supposed to get 6mb of speed and we do as long as no one is using it. However, the minute we do anything...such as streaming netflix...it basically crashes to a very low speed and even Netflix then has to buffer etc. So the internet guys are telling me it is just Netflix. Except that even when I cut Netflix off and hook straight up to the POE and test, the speed still stays down. It won't go down until we stream or download, but it won't go back when we stop. In addition, we can only do one thing at a time. The provider we had before only had speeds of about 1mb but we could still browse the web while streaming or even stream on multiple devices. So any thoughts on why it crashes when we use it and doesn't come back up when we stop? I stopped Netflix (for testing purposes) over half an hour ago and I'm still running about 1mb off the POE.