Some ISP 'speed tests' are actually be on the ISP's server and only shows the connection speed between you and the server and 'Not' the Internet. But you bought a connection to get on the World Wide Internet.
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satspeedtest.hughesnet.com/66.82.20.50
For Xplornet in Canada, The Xplornet speed test shows good on the Anikast speed test site during PrimeTime, but crap on any other speed test site during PrimeTime.
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speedtest-central.anikast.net/10.241.0.2
Your speeds are not too bad for your package. But maybe someone else could elaborate, why adding a second Idle computer causes a speed drop.
And are you on Spaceway3 KA band? HN9000 modem.. Or KU and the HN7000.