issue with combined damage types

hello,

several skill gems claim to "convert physical damage to X damage", such as "lightning arrow" and "freezing salvo", but it doesn't explicitly say what happens when your base damage also includes a different damage type.

does the other damage type get ignored, stay unmodified, or get included in the conversion to the new damage type?

"lightning arrow" is especially confusing, as its "beams" apply a second conversion to lightning damage. does this second conversion apply to the base physical damage of the original weapon attack, or to the remaining physical damage after 40% is converted to lightning damage by the projectile part of the skill? and what about other damage types on your primary weapon? do they get added to the projectile? do they get added to the "beams" (because the animation just looks like lightning damage)? and what if your original weapon already had some lightning damage on it? is this lightning damage included in the projectile and/or beams, or do they only use the damage they converted from base physical damage?

please clarify what happens to other base damage types in these cases, as there are several weapons that don't have any physical damage at all, so certain ways of answering the above questions will render these skills completely useless when using those weapons.

thanks.
-az