Clones from Mirror/Blink Arrow do not fully consider arrow/projectile-mods

The clones you create are minions that use your bow and quiver, but they do not get other items or stats you may have. So any non-minion specific nodes on the passive tree will not affect them.

If you are creating clones while using Death's Harp they should be firing 2 arrows with every shot they do, and I wasn't able to get a situation where this wasn't the case. Can you let me know the exact gem setup you were using where they weren't firing two arrows?