No, depend on the number of transaction, not fixed at 30%

You can do,

Dining (2)
Restaurant #1: RM 100
Starbucks: RM 100

Petrol (3)
Petronas: RM 50
Shell: RM 50
Esso: RM 50

Groceries (10)
Tesco: RM 20
Aeon: RM 20
Giant: RM 20
99 Speedmart: RM 20
Cold Storage: RM 20
Jaya Grocer: RM 20
Mydin: RM 20
NSK: RM 20
The Store: RM 20
Econsave: RM 20

Cash back percentage = 2 x 3 x 10 = 60%
Cash back = RM 550 x 60% = RM 330 => RM 150 (Max cap)

Anyway, optimum combination should be RM 500 with 2 x 3 x 5