> among the wages that are posted, high wage firms are more opaque, with more and wider ranges

That seems about what I'd expect. From the entire universe of job postings, I'd expect jobs at the lower end of the compensation range to have less potential for productivity differences among employees and, therefore, less range in posted compensation.

Roles with higher likely productivity variability among employees would be likely to fall into one of two buckets: variability ranging from some middling amount to very high, where firms would try to find those high-performing employees who could perform at the higher end of the range and variability ranging from some middling amount to very low, which roles would tend to have narrow ranges and companies hoping to find adequate employees to fill them and perform at the middling performance.