Where did you get the information that it should be 1300/26x2 ?
Section 60 of the EA says:
".... (b) In the case of an employee employed on a monthly rate of pay who works on a rest day, he shall be paid for any period of work:
(i) which does not exceed half his normal hours of work, wages equivalent to half the ordinary rate of pay for work done on that day; or
(ii) which is more than half but which does not exceed his normal hours of work, one day's wages at the ordinary rate of pay for work done on that day. "