[exim] Retry for Greylisting

Has anyone tweaked there retry rules to get past greylisting servers
faster? Currently I have this:

*                      quota
*                      rcpt_4xx    F,12h,15m; F,4d,1h
*                      *           F,6h,15m; G,16h,1h,1.5; F,4d,8h

Was thinking of going with 5 instead of 15 minutes for first 12 hours
on rcpt_4xx. Perhaps the receiving MTA will not like that though?

Matt