Damage of Shining Cross using element and DTE stat

SC already has light element for first hand and second element based on sub hand element.

Against dark element boss,
If we are using subhand element light, will total damage output increase (or is it useless)?, If we are using 20% dte dark in main hand and armor, will it apply to sub hand damage?

Against fire element boss,
If we are using main hand with water element and subhand with water element, will both hand damage increase by 25%? Or will it only apply to subhand (as first element is taken by light element)? Should I use element in sub hand only or both hand?

Thank you for ur guidance

P.s. I ask this because sometimes my dw gives equal dmg of sc ( for example, 245k and 245k but sometimes it gives 245k and 25k when I change subhand element [main hand element has adventage ele])

 

the damage to element boost and element is applied to the skill and not the swords. so basically its like doing 200k from each slash in sc total 400k, with the +45% elemental dmg, itll be around 590k something. with 295k in each slash idk im not good with calculations and this is just an example so ignore my maf.

The concept is basically like genshin's elemental damage. the damage of the skill is usually taken as = (attack * skill constant* skill multiplier) * (elemental damage (damage to element + element) + long range damage or short range damage)