This is likely an obvious question, but I for some reason cannot find the answer when searching. My Lelit Elizabeth, when brewing, often runs at 10-11 bars of pressure. I would like to lower this and see how brewing performs at the more recommended 9 bars. If I use the blind basket and run a 'shot' with no pre-infusion, the pressure is stable at 11 bar.

Is that 11 bar measure with the blind basket in what the pressure of my machine is set to? Is there any sort of offset, e.g., it's showing 11, but that translates to ~10 when brewing? I know how to lower the pressure via the OPV valve, but I'm just not sure, when, if trying to target 9 bar - should I see 9 bar when brewing, with the blind basket, etc?

With no flow (for instance with a blind portafilter) the pressure is the same everywhere. So the pressure shown on the gauge is the pressure at the OPV and at the group. When there is flow, there is an offset. What the offset is depends upon the resistance in the system and the flow rate. Unless there is a deliberate restriction (flow jet of some form) you can probably ignore any offset. The flow rate is so slow when running that the drop across the pipework is more than close enough to zero to ignore.

Restrictor jets get used on some machines to provide a pre-infusion effect. The Elisabeth uses steam boiler pressure to provide a limited pre-infusion pressure, so one can reasonably assume that there is no restriction in the brew circuit. Which makes the problem easy.

Ok cool - so then, it follows that if with a blind basket, I see 11, and when running a shot, I see 10-11 - the OPV is set to 11. So, if I wanted to adjust it to 9, change it so that it reads nine with the blind basket.