Just when I thought I finally worked out the rest of the code that goes in to base. Which was + % for either 250 or 300 imm exp, this char shows up.

You should not have got 60 Base, should have been 40.

The only conclusion I am left with is that there is variable not published that impacts about +20% of base. Such as manual contribution by the imms either directly or indirectly. Or could also be minus 20% button. Maybe it's hard coded for -20% if .au I am kidding!