Hi,there are two criterias for reverse charge ..
1) to pay 40% service tax of taxable value if the service provider doesnot claim any abatement (ie, SP 60% and SR 40%)
2) if SP claim abatement(abatement is 60%) thn SR has to pay 100% st on remaining...
ie,in short SR's liability is always 40% of st(4.944%)..abatement option is for SP.