How to boost reflect DMG . Add reflect DMG % affixes, the mirrored mythic , the redirect mythic, skills that reflect , electrified set . Many methods. Hero points on some skills and even talents too.
How to boost DMG in general , including reflect DMG .
WD% and ED% for DPS formula. ED% appears as ice DMG % for ice weapons and gear for eg. Also power stat 103 , high or decent base DMG weapon or a high attack speed skill or both.
Glasscannon, push the limit to increase MH% or OH% like hero points , barbarian, Crits , deadly strikes , Frostbiting ,it appears as Elemncrit in ruby and the property changes when the element changes ) , Elemental Crits, Adventurer, Momentum, Pathfinder, Demonic, Amplify, Relentless, Living force, Blindside , Darkness , Sorcery, and many others all increase your weapons damage a lot and that damage can be crit also.
Even reflect damage can crit too. Any damage can crit given enough crit chance%. Normally crit DMG deals 0 to 50% crit DMG default without having added anything . If you add 350% crit DMG, you'd deal 350% to 400% more DMG as crit than normal DMG.