Axle shims and rear blocks help

I have a 1.5" rear block in right now and I'm going up to a 2.5" block. The 2.5" block has no taper to it but I have a 3 degree shim to add to it. I know people will be burning me about doing a block and shim combo. Truth is this is only temporary just to check ride and vibes, if I'm happy I'll be ordering a tapered block to install. My question is does the shim install above or below the block? I've seen lots of installs but no one with blocks just add a leafs. And if someone is going to suggest I just go to an add al eaf the reason I'm avoiding this is because I have ride rite airbags already installed. Thanks for anyones advice.