Where's many reasons for reporting the "Ready to report"-tasks, some of the most frequent (for v7) is:

1: Client needs more work, this happens if cache-size is below "min cache size".
2: A task has less than one day until deadline.
3: A task has less than "min cache size" until deadline.
4: A task has been "ready to report" for 24 hours.
5: Project is set to "no new work".

For all reasons except #5, if client reports one or more tasks it will also include work-request if cache-size is below "min" + "additional".

So, cache-size has much to say with how frequent report results, with example cache-size 1 day + 1 day a CPU-only computer will often only report 2 times/day. With the same settings, a fast GPU-computer will never manage to fill-up to 1-day cache due to the 600 tasks/GPU-limit, so will report the results as they're finished.