Just needs a ethernet connection to the same network your Roamio is on. Mine is downstairs in a storage room were I keep my router and cable modem, only issue I have had is that I have needed to reset mine a couple times by pulling the power plug but other than that it's doesn't need to be any were physically close to your Tivo as long as it has it's network connection.
TiVo Roamio Pro
TiVo Mini (three)
Wait, if you have a Roamio, I guess it must be the Basic? The higher ones have the equivalent of a Stream inside of them (and CAN see other Tivos).. and you can even reboot it separately from the rest of the Tivo too..
(yes, it should never need to be rebooted.. but sigh.. it does..)