In the interests of balance, I understand that the 40% figure is arrived at by assuming that the majority of the high value trips (Narita etc) will be operated by the new fleet, thus cutting off some allowances from old contract crew.
The company's proposal includes protection from this loss of lucrative trip issue.
The company is offering to pay an average of all the incidental allowances for current crew going forward.
In effect, this means that even if every lucrative trip went to a new fleet, current crews earnings would be unaffected.
I think another reason for accepting the company's offer.