Since my 4Max Pro has much too little fan power for the part cooling, which is caused by a firmware limit (M106 S177 is already reported as 100% but only supplies about 10.2 V to the fan instead of 12), a cheap original fan and a much too small opening I decided to fix the latter which is easiest to do.
I cut off about 3 mm from the bottom of the original fan duct which results in an opening more than twice the size.
Now more sagging Benchy bow.