I'm not confused about anything chaps.
Lets assume VFE of 240 kts at FL200. Around 320 kts TAS.
VFE of 240 kts at FL380 equals about 450 TAS.
A much higher TAS and therefore Airload on the devices.
Naturally you'd have to be close to VFE during cruise at FL380 otherwise you'd be below Minimum Speed. ( in most heavy jets anyway )
That's all.