IATSE budget tier calculation

European here trying to get my head around the IATSE agreement:

The definition of "production costs" in the 2026-2028 Low Budget Theatrical Agreement seems quite basic, and I keep seeing references to a "sideletter" which defines exclusions and so on to calculate the production cost. For example here: https://cmsproductions.com/blog/production-savings-iatse-low-budget-theatrical-agreement/

I would love to double check this by having a look at the actual text, does anyone know where to find it?