Visual C++ :: Throttle Binary File Download Via WinHTTP Gives Unexpected Results

My Windows service may download a binary update in the background using WinHTTP APIs. I'm using code similar to the one from the bottom of this MSDN page. For ease of access I'll copy if below:

Code:
DWORD dwSize = 0;
DWORD dwDownloaded = 0;
LPSTR pszOutBuffer;
BOOL bResults = FALSE;
HINTERNET hSession = NULL,
hConnect = NULL,
hRequest = NULL;

[Code] ....

The issue I'm experiencing is that while downloading, the code above "hogs" most of the bandwidth available on the client computer. My goal is to make it "throttle" itself on a configurable "bps" level, say at 50 kbps and not use any more bandwidth.

Someone suggested measuring my current download speed (in bps) and depending on the value make the thread "sleep" before calling WinHttpReadData again.

So the formula I'd use to calculate BPS is this:

BPS = (BytesDownloaded * 1000 * 8) / TimePassedInMilliseconds;

Then to convert to Mbps:

Mbps = BPS / (1024 * 1024);

And the waiting/sleep would be done as such:

Code:
DWORD DesiredBitsPerSec = 50 * 1000;//for 50 kbps
if(fBps > DesiredBitsPerSec) {
DWORD dwW = (DWORD)((fBps - DesiredBitsPerSec) * 1000) / DesiredBitsPerSec;
if(dwW > 0)
::Sleep(dwW);//Sleep to throttle the download speed to the one we need
}

So I implemented it into the code above but it didn't work -- the Sleep API would produce very strange delays. So I decided to add a little bit more tracking code to actually be able to see what BPS values I'm getting.

I created a small test project that is attached to this post to illustrate the issue. (It's hard to explain without running an example.)

For a test I began downloading a large binary file (Windows 10 MSI, off Microsoft's server) and at the same time had the Task Manager open on a Performance tab that was showing me the current network throughput. I made a screenshot:

But as you can see, the reading on the test program and the actual network BPS values differ greatly.