Hi,
Can you post the screen of your report?
Just an idea, how about converting your fiscal period or any date char you are using to KF using the blog below..
Convert a Characteristic into a Key Figure (BEx)
Afterwards, I will create a formula and do an IF condition so that fiscperiod jan 2016 will just get the 3% and feb 2016 onwards will get the 5%..
Sample IF condition: (assuming that you only have 2016 data onwards)
(FISCPER = '2016001') * (KF * 0.03) + (KF * 0.05)
Regards,
Loed