Dynamic envelope on drums

Hi everyone, sorry if this is a stupid question, I’ve searched the forum and looked at the manual and can’t find anything.

When using the dynamic envelope on drums I can’t make a convex curve (Or a straight line) for attack only a concave curve. The picture in the manual shows a shape I can’t make. I’ve tried shift + different coloured knobs but nothing. Green only seems to bring the whole lot up or down too.

Hopefully I’m just missing something simple. Please help!