• The Cooler Master Hyper TX3 EVO heatsink is just right for your micro, not to mention short.
• Your graphics card, not having an official heatsink, dissipates heat inside the case instead of coming out the back.

Conclusion: your case is too short because even if you put a bigger heatsink, you will only improve temperatures when using only the CPU... if you use CPU and GPU (games) you will have those temperatures no matter what you put because the hot air from the graphics card goes up before leaving the case.

Solution:

• Run both the CPU and GPU through OCCT to see separately how each one heats up. Then run Prime or AIDA64 in FPU mode while running OCCT on the GPU (that is, stress both components at the same time as a game would).
• Once you know the temperature each component can work at inside the case, mount everything outside the case and test again to verify that you don't have a temperature difference greater than 5 or at most 10º compared to having it mounted inside.
• Last step:

Too big difference when mounted inside or outside -> change the case
The CPU gets too hot and thermal throttling appears or crashes the screen -> change the heatsink
Both problems ->> change both

Salu2!