I would assume that if you have two lines with the same grain weight but one is longer - ie if you had a WindCutter (approx 54 feet long) that had a head weight of 600 grains and a MidSpey or TT that have head lengths closer to 70 feet that also weighed 600 grains - these two lines would cause the same rod deflection (ie load the rod the same??)

I think the shorter belly would load more suddenly and perhaps feel heavier because of that.

Personal opinion but I think Carl's on the mark from my experience. The stiffer the rod, the more "weight forward" the line. Softer/flexable the rod the more I want the line wt. to be spread out. But that (as they would say) is my 2 cents.

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