A silicone sock on the hotend will help a lot.
I should be ordering a few supplies soon, and I will get some socks. My little Ender 3 has one I noticed.
If your duct is blowing on the hotend directly that will certainly have an effect.
I studied the design of the fan shroud outlet ports, and it does look like the designer was definitely trying to direct the air down on the part, and not toward the heated block.
On the subject of this layer cooler: I decided to reduce its output. I thought of a really easy way to do that since it's powered by a 40mm x 40mm fan bolted to a fan mounting port. I just put some washers between on each of the four screws. Now some of the air escapes through the four narrow slots created, and the flow is a bit less near the hot end. If I want to reduce it further, I can add four more washers.
I would expect the reverse situation.
Not sure about that; those are just the auto tune numbers I got. It's the stock FT-5 bed with a piece of mirror glass on top.
In an effort to get things stable enough that I would not have those "in excess of the 15 Deg C" overshoots that were causing faults, I tuned it again using 0.8 for the PWM parameter. I got a new set of numbers for the M307 command. So far so good insofar as the part that aborted yesterday evening looks like it's going to finish today.