Hello Cjkeller

                        About the speed check on the Surfboard central app, yes it is designed in such a way to check the speed of the devices using modem network since this is just a application, but to find the optimal speed that your modem is getting from your Internet service provider can be done only on direct connection, hardwired to the modem ethernet port, so we would suggest you to check on direct connection to find the exact speed of what  your modem is getting from the ISP.

Let us know if this helps.