Inconsistency with Ahri's ult damage to enemies originally in Fog that gain vision from the dash

So, I died yesterday when I ulted over a corner to get the last piece of damage needed to kill an enemy Xin (he had like 40hp, guaranteed to die from my ult, I landed right in front of him after going over the corner and the ult did no damage, all my abilities on CD and he lifestealed harder than I could auto attack him).

So I went in to practice tool to see, does Ahri's ultimate do no damage to enemies that were originally in the fog of war, but I gain vision from the dash? The ability clearly specifies that ahri dashes first, THEN shoots the bolts at her enemies, so from the ability description it SHOULD do damage if I gain vision from the dash.

So I placed enemy target dummies in fog of war and tried ulting into them. The result was quite surprising. About 2/3 of the time, my ultimate did damage. About 1/3 of the time, it didn't.

It largely seemed that if I gained vision only towards the end of the dash, or possibly even only if the complete length of the dash wouldn't have gotten me there and I was using a wall to create extra distance, it dealt no damage.

If they were standing in brush and I ulted from near the brush directly into the brush, it dealt damage nearly every time. If they were over a thin wall and my ult easily cleared the wall, it dealt damage every time.

This seems really inconsistent. My ult should either ALWAYS do damage if I have vision after the dash, or ONLY do damage if I have vision before the dash. It shouldn't be this random guess, because then you end up making boosted plays like I described at the start.