Why not ask those making the claims, to support those claims with evidence ? Presumably they have done lots of testing ?
But generally it refers to pre-turbine pressure, not post turbine, but of course all play a role and in general the lower the better.
But if you're running say 30psi boost, it would be entirely reasonable to expect 30-50psi pre-turbine pressure under high load/rpm depending on setup. In some cases you can get pressure ratio below 1:1 but for most part it would be higher.
I'd imagine many OEM turbo setups run pretty high PR's, but they'll use small turbines that spool very fast, so there is always a tradeoff somewhere.