[[3-2]] working but not -1

This in relation to the Pathfinder Sheet, specifically Buffs. I wanted a system which increases a size to the next scale. Since I can't have two things saying +1, since they'd just overwrite eachother I decided to do something else. This is only for going from Medium > Large > Huge. It breaks down after that. So @{size} can be used to call the overall Size debuff, since it's a negative to AC. If I try to do [[@{size} * -1]] in a Macro it works fine, but when I move it into the auto-calculation of a Sheet-Buff it breaks down and just returns 0. However if I do [[@{size} * [[2-3]]]] it works fine and returns the expected result. Does anyone know what causes this? I can work around it, but being able to avoid it is better.

I've actually found that this is recursive, so it doesn't actually work. Does anyone have a way to have two seperate buffs, that increase your size to the next scale? ie if one is active it's Size increase 1. If both it's size increase 2. It can't just be the one move large and another to huge, has to be variable.

I assume this is the Community sheet?  Size is included in the buff section. You can create a buff(s) that changes size increments up or down by "x" number when enabled.  These buff's only effect the current value of size up/down.  Where are you applying your macro(maybe a screenshot would help) and what exactly are you trying to accomplish(maybe a reference link)? Thanks