the whole premise here is that there is some correspondence between this rate and the negotiated rate
That is a plausible but false assumption. Different providers negotiate different rates. In many cases, the negotiated rate for a given provider is lower than the "cash rate" that an uninsured person would pay, but in many cases the negotiated rate it is actually much higher(!). Maybe in these cases the insurer gets an end-of-year volume-based discount that the insured (me) never gets to see.
Source: my recent experience shopping for an MRI while on a high-deductible plan.
That is a plausible but false assumption. Different providers negotiate different rates. In many cases, the negotiated rate for a given provider is lower than the "cash rate" that an uninsured person would pay, but in many cases the negotiated rate it is actually much higher(!). Maybe in these cases the insurer gets an end-of-year volume-based discount that the insured (me) never gets to see.
Source: my recent experience shopping for an MRI while on a high-deductible plan.