I found a part in the settings of the bracing table - under custom settings ->Achieved BUs -> Along Number & Type -> Length Height & BUs
where i was able to change the length of the brace line to what i wanted, and this updated the table automatically - but when i updated the bracing table from the cadimage menu - it changed the values back to what the were before.
I also noticed that in the 'Length Height & BUs' setting - it shows the correct BUs/m - so why cant it show this on the bracing table?