spacer geometry question

My truck started out as a show truck on the dealership floor where they threw a bunch of glitter and nice things like rims tires and a lift. It didn’t sell so they traded it to a dealership near me, I showed up the day it got in and had no problem taking it off their hands. Doing my research ive discovered it has 1” blocks in the rear but I’m unfamiliar with the lift the front spacers are giving me. I measured 2”s but somewhere on here I read that spacer lifts lift the truck double the size of the spacer. Due to thermal dynamics or Einstein’s principal of theory… maybe something to do with flux compacters…

Can someone explain this to me so I know what I need to run my tires with. “285/75-18 toyo open country M/Ts”