I was told by a local farmer (with big free range units) that all the commercial layers that look like the above are based on a "Warren type" bird. They produce different strains at times and give different names eg. hylines, lohman browns but all basically very similar.
I have hybrids that look much the same as yours. Some were described as warrens, others as hylines.
Before reading your text, I did look twice at the tail.

Does seem longer and more upright than most of mine over the years.