I don't own every 386 motherboard out there, so I cannot say for certain if the reduction by 1 mm will help. I am talking about all 4 sides, not just the FET side. I have on a few occasions had upgrade adapters just barely not fit and it is irritating. I either have to desolder a cap on the motherboard and replace it with a smaller one, bend the cap out of the way, or have to use PGA extension sockets to make the clearance.
The other adaptor I have, same one that the other poster just provided a photo of, I use it with an additonal VRM module, and on one baord, it just barely hits the reset header on the motherboard. So I had to use an extension socket to make the clearance. In such a case, if it was 1 mm smaller, I wouldn't have to use sockets to lift up the board.
It may only be worth the effort to shrink the board by 1 mm on all 4 sides if something else of greater importance needs to be changed on the design.
Luckily, the 1210 ceramic capacitors I ordered will fit the existing design, as well the smaller 1411 tantalums. Just barely, but enough that solder won't have to bridge an air gap.
Plan your life wisely, you'll be dead before you know it.