Ruling on bomber targeting a space instead of an enemy for dealing splash damage
I'm a relatively new GM running Age of Ashes and I have a player playing a bomber alchemist, and the situation has come up in multiple combats of them wanting to target the space by enemies instead of the enemy themself for the purposes of dealing splash damage. The original ruling I made was for an attack roll (as critical misses do not deal splash damage), but then came the question of which ac was to be rolled against, noting that if a typical AC of floor was used that it would be pretty much impossible to miss.
After considering it a bit more, I think I'll change my ruling to give enemies in the target area a basic reflex save against the splash damage using the dc calculated from the attack modifier (and including range penalty, MAP for DC, cover as bonuses to the save). Does this seem appropriately balanced? Alternatively, is there a ruling made in the books that I've missed?
Edit: Regarding why the player is choosing to do this, they are primarily using their versatile vials to do this and using calculated splash to have it deal 4 damage, and with quick bomber it is a supposedly guaranteed 12 damage per round to each enemy. It also probably has to do with my bad habit of buffing enemies such that the ACs are high relative to level, and said player's perceived bad luck on attack rolls.