Pressure on the measuring devices is NOT a constant save for the basic factors. Other parameters also have to be factored. Thus `position` does have an effect. And oxygen level impacts on INDICATED air speed as one of those factors - a direct cause of the pressure effect that sees IAS reduce as altitude and pressure density increases.
By all means correct me when I'm wrong. This is not one of those times.
Provides a reasonable technical explanation of the derivation of IAS, which is a calculated result, not a simple reflection or measurement. It also specifically refers to position error.
I think on that basis I'm going to use that technical document rather than your own opinion as a correct statement of the actual state of affairs.