I think you're right. With the caveat that I don't grow outdoors, I think there is a significant difference between the effect of a minimal light change indoor vs outdoor. Maybe Shed is right about the flip to flower beginning on the summer solstice with the most minimal reduction in light hours. Outdoors.
But that's not what we're talking about. This is an indoor, one time change, not a gradual and consistent degradation in light. You're doing it in one step and then leaving it to be the new normal. And, as you said, you are far from even the 12/12 commonly used as the indoor standard setting.
Maybe if you did it mimicking nature over a period of a month or so the plant may begin to get the message that fall is coming, but with a one time, step change indoors I think it won't miss a beat.