Taxes calculation Issue in salary slip

Dears
we have made a payroll period as below

and an income tax slab

also we have created a salary structure with a sample two components basic and income tax

but only January salary slip has been correctly calculated which is

basic = 3000 * 12 months = 36000 annual

Net tax applicable = 36000 - Tax Exemption 9000 = 27000

first tier with 0% tax = 15000

next tier = 27000 - 15000 = 12000

taxses = 12000 * %2.5 = 300 Annual / 12 month = 25 which is right

but other entire salary slips for months 2,3,4 and 5 not probably calculated !!

any idea ??