Ignivar’s Head unique ashen skull appears to be tailored for Disintegrate, as it adds 40%-60% increased fire damage, Disintegrate deals more damage equal to your spell crit chance & 50%-150% chance to ignite on hit while channelling.
Unfortunately, since Disintegrate has the DoT tag, it can’t hit & therefore can’t ignite (or shock).
Please could you remove the DoT tag from Disintegrate so it can hit stuff & therefore benefit from Ignivar’s Head, Cinder Song & Calamity’s various ignite on hit lines. And it would be able to crit which would help it’s damage output.