AoE cannot trigger head shots or work with Aptitude. Just go for a balance of big, consistent crits.

You can put whatever you want in the exilus slot. Terminal Velocity matches the polarity and will improve projectile accuracy a bit. The Lenz has a built-in "[Arrow Mutation]" effect, so using something like [Vigilante Supplies] will only gain you the 1 in 20 chance to enhance crit tier while costing you another forma.

Updated to use Primary [Frostbite] for maximal output. Overframe does not accurately [Reflect] the gains from this Arcane with [Hunter Munitions]. The net gain is that it will be increasing the number of slash procs (via multishot) and the severity of procs (critical multiplier) with every target hit by the AoE and forced cold proc.

If you want to target a specific faction, replace [Serration] with a (Primed) Bane mod.