The purpose of a heatsink is to draw heat from the chip to a larger surface area, So the ambient air can dissipate the heat.
https://www.techopedia.com/definition/2211/heat-sinkWith that said and the limited space on the motherboard.
I would say a higher circulation of air is needed.
Meaning find a replacement fan with the higher cfm. Or change the bios setting to ramp the fans up faster per temp increase.
Both of the options probably mean more noise.
And the bios settings for the fans are on two separate pages in bios.
One page you disable the defaults.
If you don't disable this all your fan settings will be lost when you reboot.
.
The other page is where you set the PID scale with gain.
Gain is the initial speed at boot which currently should be 100%
The others are Proportional which is the target minus the actual
The integral is the sum of the error over time just to bump it up a bit if Proportional does not meet target..
The Derivative is the opposite of Proportional somewhat to help from overshooting the target