If the mast bend makes the blocks closer together (lowering the clew), then it will change. But, for most boats the downhaul does not significantly change the relativity of the sheeting blocks.
Rick
Disagree.
When applying DH you are streaching the sail and bending the mast; this will change the sheet position.
THink about what is ahppening; mast bends and sail flattens (top of the sxail falls away); to get the sail back into a good foil, you have to pull more leach tension; this means more mainsheet.
When sailing without any extra DH, I have about 20cm between the blocks on my F16; when sailing with full DH (but needing to sheet in) my blocks will be almost block to block.
