Believe it or not Trane Application Guide SS-APG001-EN says "to slope 1/4" to 1" per 10 feet of run toward the evaporator"
We were installing some 80 ton splits about 15 years ago when i got this. I took issue with it and called engineering, they said yep if you install our equipment that is the way we want it done.
There is a lot of other good stuff in there too, about P traps and such.
Remember this is for their system
Slope in pipes towards compressor is so important for oil return. I had an opportunity to repipe a 10,000 sq ft freezer that was not properly sloped. Before the job we constantly had oil problems and endless compressor failures. Afterwards never lost one compressor! It was an older system using Carlyle 5F40 compressors. It took some time to convince the customer it was a major issue with his system. Now he is my best customer and sends me tons of referrals.