It's not a flaw in my assumption. Although I think you are probably doing what I was trying to describe. One needs several headphone sets as reference to be able to properly apply a scale across a range of values and do it consistently over time. Audio memory is too unreliable to base such different ratings on with one reference headphone set. Too easy for someone to assign a different rating to a headphone that should have deserved the same as a previous one.
And still, I might not trust your ratings against each other even then unless you are a professional reviewer doing it regularly. It's nothing personal, but even people that regularly try to apply a rating scale have to be careful to do so consistently over time when it comes to subjective evaluations. That's just a known issue with rater reliability in subjective evaluations of all kinds of things, and it has been discussed plenty in qualitative assessment and evaluation methods. One must continually work to keep one normed with ones original evaluation scale.
I'm doing that now. Finally got what I can call a Mid Fi refrance Closed can to compliment the DT 880 as my open. So from here out just need lots of head time