This message was posted on behalf of Intel Corporation
Based on your description, the behavior you are experiencing is completely expected and let me explain you why; this is because this feature will be reached whenever the processor needs it. Intel® Turbo Boost Technology 2.0 accelerates processor and graphics performance for peak loads, automatically allowing processor cores to run faster than the rated operating frequency if they’re operating below power, current, and temperature specification limits. Whether the processor enters into Intel® Turbo Boost Technology 2.0 and the amount of time the processor spends in that state depends on the workload and operating environment. Due to varying power characteristics, some parts with Intel® Turbo Boost Technology 2.0 may not achieve maximum turbo frequencies when running heavy workloads and using multiple cores concurrently.
More information can be found here: Intel® Turbo Boost Technology 2.0