there is a situation where the dsl face plate compaired with a normal microfilter with no extention wiring off the master socket can make a difference.
If you have very high db attenuation loss ie over 62-63db. I've found on the very odd occasion (and this seems very rare) when the full plate will get sync yet the standard microfilter won't.)
This is only If your set on a genuine 0.5mb fixed speed service. and teatering right on the limit. and you fit the above situation exactly. I'm a bit guarded saying this as I don't want people to go running with £10 out getting the plates in order to get sync. If things are getting that bad then you really need an engineer to come out.