just obviously it shouldnt take 15 minutes for a monster to respawn >.>
2 Iron Bucklers: 1 - (1-0.6)(1-0.6) = 1 - (0.4)(0.4) = 1 - 0.16 = 0.84 = 84% to block 20 damage; 0.84 x 20 = 16.8 average