TEST YOUR HOOKLENGTHS
ONCE you are happy with your reel lines matching the various rods you own, try the same exercises with various length hooklengths. The further away you are from the end, the more stretch factor you have and that allows you to use thin diameter lines.
Obviously, there is a problem if you hook a big barbel or carp on a very light hooklength but if you are fishing on rivers where there is little chance of this happening, you are better off using lighter lines to get more bites from smaller fish. For my lighter action float rods I use hooklengths from 0.10mm to 0.16mm and for stronger rods I use from 0.18mm to 0.21mm or tie the hook direct to the main line.