It depends what quality cable connects the extension socket to the master socket. With normal telephone extension cable the answer is no.
But the modem and your router do not need to be close together. They are connected using standard ethernet cable, with a maximum distance of 100 metres.
The basic setup is with the FTTC modem connected to the master, which has an interstitial faceplate fitted to filter the phone and VDSL2 signals, using just the short VDSL cable supplied. See this pic
There is a "Home Wiring Solution" (also called a Data Extension Cable) that you can order at the time you order FTTC. Some ISPs order it for you automatically just in case it is needed, others don't.
With that cable, (instead of normal stuff), the engineer can site the modem up to 30 metres (internally or externally) from the master socket and install a socket for the modem to connect to. But that means him fitting that cable at installation time and you might not like the look of the result.
Alternatively, using the same new cable, he can move the master socket to a more convenient place.
My broadband basic info/help site - www.robertos.me.uk
| Domains,website and mail hosting - Tsohost
Connection - Plusnet
UnLim Fibre (FTTC). Sync ~ 54.3/15.4Mbps @ 600m. - BQM
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