Material account hitting while posting Excise Invoice for dealer

hi

i have a problem in posting the excise invoice for dealer

PO base rate- 160 including excise

PO vat-12.5%

when i do migo for 615 qty & capture the invoice by changing the excise value as per invoice with mrp indicator flagged the entries as follows

Stock account - 83087.24

Gr ir clearing -83087.24

while i do miro, with tax code different from PO, here tax code(excise + vat ) the entries were

vendor account-    127927

Gr ir clearing -       83087.24

material account-15312.76

cenvat clearing-15312.76

input vat-14214.10

why the material account is hitting? GR IR amount is lower than the PO base price