ACD lower on Ast 1.8?

I inherited a network that does have 10 Asterisk servers, these servers do have Kamailio Sip proxies in-front of them and use A2B for billing. Currently the Asterisk version is 1.4, but since 1.4 is EOL I need to switch to 1.8. I did install a new server, all other settings being the same and same A2B version the ACD of 1.8 is always lower by half a second. So if the ACD average is 5 all 1.4 are around ACD 5 and the 1.8 machine ACD is around 4.5. I have noticed this over a week and I can not find any error messages that would prove why this is happening or provide a reason.
Has this happened to someone before ?