One thing to remember is that it is perfectly normal to develop two "low spots" where your bones go on the saddle. That is the saddle breaking in to fit you (as the folds and wrinkles of a shoe would do on your foot once the shoe breaks in). Tensioning is not done to get rid of those low spots so much as to reduce the amount that the whole top sags when you sit on it. The top should have some give to it, but should not sag all the way down on the frame - something different from the particular low spots where your sit bones go. If the whole thing feels kind of "soft" and saggy, then tension, but do so carefully. I love my Brooks Flyer (the B17 with springs), but my heart still belongs to the B66.