That's absolutely true, the board can scale back if the offer is...

That's absolutely true, the board can scale back if the offer is oversubscribed. But that doesn't translate to "the board has discretion over who gets to participate in the SPP and how much they get". If they choose scale back, they have to scale back in a way that is consistent with the terms of the offer. They don't get to pick and choose arbitrarily. Every eligible shareholder gets to participate if they lodge an application. And if there is a scale-back then every shareholder who apply for more than the minimum allotment gets scaled back in a consistent manner.