The ICOM knowledge base available at Icom Global has a document on digital settings.
The power control on most ICOM radios DOES not control power out. It sets the power out threshold.  Max power radio will put out.

Set power out for 100% then adjust slider while watching radio power out meter to set the desired output power.
As long as ALC is in green all is well

No ALC for digital is one of those ham radio myths. It does not apply to constant carrier signals like FT8

FYI on Elecraft radios ALC does not operate until ALC reaches 5 bars. 
Ray
W8LYJ