meth injection set up info needed

[GuillaumeC]

explain "post-tb" like right behind the tb?

Not necessarily right behind, but anywhere in the intake manifold where the reference line or sensor will see vacuum and boost.
The pressure sensor needs to see vacuum as soon as the TB blades close to shut it off immediately.

If you get the boost reference signal from the charge pipe or compressor housing, there might still be some pressure there even after the TB blades close. That would keep the water/meth on for a second after the blades close and can cause sputtering. It was a problem on my car at first and a friends turbo Mustang. Connecting the reference line to the manifold fixed the problem.