The rake bonus you are thinking of is from the advanced rules, the gun factors are given in two values eg 2(6)where 2 is the factor for normal shots and the 6 is for rake(25 guns at range 4), the +1 you refer to is the additional modifier for a stern rake (the stern is flat not pointy like the bow, large amounts of it is glass(captains quaters) and therfore a stern rake was more devastating than a bow rake)