I did some test and find that boards width do not increase sailor moment to sail.
On internet common picture shows like this:




From this formula comes, that wider boards have longer lever arm ("b" on this picture) which sailor weight act on sail heeling moment,here means wider boards take more force from sail because sailor is staying more out of center line..

People always forget that board is connect with sail with universal joint,so universal joint can not take moment force.
This picture works only for sailngBOAT,where mast and hull is "one body" and moving together..
SAILOR CAN NOT TRANSFER HIS WEIGHT THROUGH BOARD TO COUNTER ACT SAIL HEELING MOMENT,BECAUSE BOARD CONNECTED TO SAIL WITH UNIVERSAL JOINT.
Sailor transfer his weight to sail only through harness line (90%) and arms (10%)

Empirical test
I am 90 kg,first I step in foot straps,hook in and max lean back and tension scale shows about 30kg.Then I move 1 meter out of foot straps,(like I sail with very very wide board) extend my harness lines and tension scale still show about 30 kg..











imagine mast connect with universal joint ,and fulcrum under joint...

What is magnitude F1 and F2??

in both situation the same...