Your basic premise is right, but perhaps you are looking at "ineffectual" from a human, earthly perspective rather than a divine one.
If I am damned, can we say His sacrifice is ineffective because I am not saved? I don't think so. It is still perfectly effective because it was an act of perfect love that would have redeemed me had I lived up to it.
It is like calling a 9-11 firefighter ineffectual because he never pulled anyone out of the WTC. The sacrifice still stands. The heroic charity is still evident. In the economy of love (which I think is as close to God's view of things as we get), it's actually quite immaterial whether he pulled anyone out or not.
Just a thought. Predestination is not a strong suit of mine.
But he WAS ineffectual. We don't question his heart, or his character, but that doesn't mean we can't acknowledge that his efforts failed to produce results.
I don't see how any human could snatch themselves out of the hands of God. Nor how any human could render a sacrifice which PAID for their sins ineffectual. If a man walks into court and pays your fine, you are out of jail, whether you "accept the help" or not. But if you COULD reject the money, then the money would never have been GIVEN, and the attempt would have been a failure.
Since the act of sacrifice of Jesus was a perfect sacrifice for the sin, how could any sin still have any punishment left to be rendered, for which Jesus had already paid?
This plays into an argument about the surety of salvation as well. If one COULD snatch oneself out of the hands of God, it would have to be because God allows it. But if God only chooses those whom he knows will accept his choice, why would he put anybody "in his hand" who He knows would later reject salvation?
Sorry, I guess I'm falling into the trap of adding new parts to the discussion, which might well get us off track.