Setting tax exemption limit through PCR

Dear Experts,

We have international payroll for Kenya, now requirement is to set Tax(Paye) exemption limit 20000 comprising NSSF, Vol. NSSF, Pension, Vol. pension and accordingly computing net taxable pay.

Now to achieve it i defined a constant ZPEXM in T511K as 20000 and tried to compare this constant through a PCR, so that my tax exempt wagetype /192 can be properly populated. we have two variable wagetype, 4PTE for Pension and Vol. pension, 4NSF for NSSF and Vol.NSSF, created a new variable 4PEX for tax exemption limit. Now PCR is like below. Now it worked upto first part i.e. 4PEX computation, but second part i.e. ZPEXA didnot work. My purpose is to compare 4PEX with PEXM constant, if > then /192 should populate amount upto 20000 and rest amount should be added to Net taxable pay 4NTX.

Please someone help me to achieve it.

Thanks & regards

Tandrima