In September, the closing price on the night that the SPO was announced was 28.65. The subscribers had a purchase price of 27.60 (28.65-27.60=1.05; 1.05/28.65=3.66% discount), and AGNC received a net price of 27.02 (2% discount to underwriters).
Using the same discounts as the last SPO would suggest that the pre-SPO price be a minimum 28.51 (26.90/.9434), in order to break even with the MRQ BV/share of 26.90.
Current Book Value/.9434 == $28.51 for breakeven. But i'm thinking above break even. Last anouncement was at a stock price of $28.65 when the book value was 0.14/share less. If you add $28.65 +0.14/share = $28.79/share trigger SPO