Endless Munitions doesn't affect Skeleton Mages

Endless Munitions doesn't affect Skeleton Mages.
The wording suggests that it acts like a support for multiple projectiles - which does work.
This kinda blocks Deadeye from being an effective projectile-minion ascendency.

I'm shooting from the hip because I don't play with this notable (and don't happen to know how it behaves with Mirage Archer minions),

but I suspect this comes down to the Deadeye ascendancy granting +2 projectiles to "your skills," while your mages have their own minion skills that are not affected by your ascendancy.

That is, Summon Skeletons of Mages is a skill you use that simply summons the mages. It is not a projectile or a bow skill.

The summoned mages use their own skills to fire projectiles. If they were in a link with a support gem that granted extra projectiles, the minions would benefit from it (as they do with GMP). However, in this case there is no support linked to the minion skill for them to attach their own skills to.