His Royal Highness –
Fine but Brooklyn in area is greater than twelve mil by twelve mil. Rav Moshe follows the Shulchan Aruch and requires a daily shishim ribo (see 4:88 regarding the beaches). Consequentially, we still fall short of 3 million. (I would also point out, there are other reason to allow our eruvin according to Rav Moshe such as the mechitzos encompassing Brooklyn.)