Hi OP… I think you are fairly local to me if I have the right guy in mind…. down in Kent.
I have set a target of 60 off road miles a week (3120 for the year), this may not seem a lot but through the winter it has taken a fair bit of determination.
I am currently on 782 miles (1258km) which is 7 ahead of schedule apparently! There is some 17900m of climbing in there too…. not sure if that is a lot, mostly I ride on undulating terrain.
It has been enough to see me come into the spring in fine form and setting the target has motivated me to go out when things have been pretty grim.
So yes I set a target and it helps but it is all just riding my bike….
For the record, BRs rides are damn hilly!!