This question comes again and again.
Bar pressure is:
1 The force needed to keep the kite and certain angle of attack when kiting.
2.The force needed to turn the kite.
Light bar pressure means less force needed. Changing the bar pressure with different wingtip attachment points has the following simple explanation:
Imagine the kite is a simple leverage system where the front line attachment point is the fulcrum and the rear line attachment point is the place where force is applied (for simplicity no bridles are used and the from lines are also connected directly to the leading edge).
When the rear line is attached closer to the wingtip (setting A on Cabrinha kites), which means further away from the front line attachment (fulcrum), you need less force to keep the kite at certain angle of attack. You also need less force to turn the kite (change angle) BUT you need more travel! Simple physics!
On the other setting B (away from the wingtip, closer to the fulcrum) you need more force BUT when turning the kite you also need less bar travel to achieve the same change of angle!
Same bar travel has more effect on setting B then setting A.
Since the travel is fixed bar fully sheeted out will allow a little bit more "De-Power" on setting B.