18' trim tab location

[1Step]

I need your guys help on this.
I have a set of 12 x 12 Lenco tabs I'm putting on the 18.
I can get them to fit on the outer strake(sp) but about 2-2+1/2" overlap into the middle one due to the scupper location blocking the tab from being flush to the outside edge.
This means a small portion of them will not be contacting the water as much as the main part does.
From what I've read, the farther out they are, the better they work.
I can move them to the middle one and have the complete 12" in contact with water.
Lenco says the small amount doesn't outweigh the benefit of being as far out as possible.
What do you guys recommend?