Most of SCH cast surcor just a few seconds before you pull the boss, is a habit I have seen in almost any hard and extreme runs I have been, if you use shieldlob then provoke you will have almost guaranty than you will have full agro and some time to star with your rotation, flash is useless at extreme 99% of the time, except maybe for the blind effect, funny thing if you cast stone skin with full hp or pop a cure it also generates extra enmity, weird but works