Imissmy3rdgen7 - heat-soak is much more pronouced on forced induced cars.
For simplicity sake, turbo cars have higher throttle body intake temps vs a N/A car in the same environment. To combat this, an intercooler is introduced into the plumbing before the throttle body. The I/C is designed to cool the air from the compressor of the turbo to more "liveable" levels before being ingested into the motor to mix with fuel & spark to create power. When the I/C becomes saturated with heat (ie: from increase boost levels, poor conductivity, poor flow characteristics), the temperature out of the I/C increases. Hence this makes the motor more prone to knock. Cold dense air gives more O2 molecules for combustion, the hotter the air, the less the O2 concentration. Hence a sign of heat soak is power loss.
A 2nd sign of heat-soak is "sluggish" performance. Especially after the car warms up, you turn off the car and go again. You'll feel more "lag".
The above is just a simplified explaination. There's several other symptoms of heat-soak which are more technical.