composition levy

Bit confusion in the definition of
aggregate turnover 2 (6) & Turnover in state or turnover in Union territory 2(112)
as composition scheme can be opted by only that supplier who is not engaged in inter state outward supplies.
while rate for composition levy is 1%/2.5 of turnover in state or union territory which defines that it includes inter state supplies of goods & services made from the state or UN by the said taxable person.

so my question is if such supplier is involved in inter state supply, how can he opt composition scheme ??