reliably predicting future experiences E2 in a range of contexts C (as C approaches infinity) consistent with the past experiences E1 which led me to to put X in my model in the first place.

I wholeheartedly approve of this approach. If more people used it, we would avoid the recurrent unproductive discussions of QM interpretations, qualia and such.

EDIT. Just to clarify, the part saying "put X in my model" is the essential bit to preempt the discussion of "but does it exist outside your model?", since the latter would violate this definition of "exist". such as this statement by our esteemed Kaj Sotala:

why those beings actually have qualia, and don't merely act like it.