Can XP Pro Fax be set to answer only on multiple rings

OK, so I can’t find an option to do this which I presume means it can’t be done, but I have recently installed XP Pro on my computer and would like to set up the fax bit so that all incoming faxes are routed to my computer. I have two numbers that work on the same line and even if I set one of the numbers as a fax, the modem will answer for the other line (the one I use for voice) every time. Can I set it to only answer on multiple rings?

Or perhaps, I should set it to answer only after 5 rings (as the answering machine picks up on four)?