You are using a MTL tank, they are designed for lower watts. If you want to up you watts get a new tank or rda that can handle it or design for higher watts (With airy airflow)
@Shatter I don't necessarily have to up my watts; I'm just puzzled why a device CAN go up to 40W, but burns my throat if I go higher than 20W. Curious ... puzzled ... seems like such a waste.