You are close by using 5% for today, discounted for FN & governments. I lean towards 10% because feasibility is done and we are well past that. 10% representing feasibility stage.
But my valuation is as if we were producing today and 50% is fairly conservative. With today's price $450/ton and subtracting about $120 per ton for operating and over head (taxes, royalties etc.) we still get over 300$s per ton. That could reflect 70% or so.
The post is for people hoping similar to Crazydik, who are not considering value today but what it may be once we are operational and dividends flowing to investors. In other words, what might be the maximum sp some day.