I believe that is for whats called road crown which is the slope of a road surface to the outside for proper drainage. Reducing caster on the left front wheel is sometimes used to compensate for road crown.
To the OP- If it was my car I would max out as much positive caster I could before the control arm hits the subframe and no bias. It will help keep you going in a straight line when it gets loose with all the torque the dark side has to offer.

 

bias? The cars a pure drag car (very very light street) so im gonna move the top plate to get more caster but i would assume the strip i would have no crown unlike a standard road

 

You wont get much if any caster from moving the stock strut top. Its all done with the tension rod you built. Also you will be lucky if you see 0 camber from moving the strut top. It will still be positive. I would put the strut top so it favors D in Fig 10-33 on the diagram posted for both sides. The bias caster thing to one side was just me speculating on the factory specs. Not needed ever unless you like to drive with no hands on the wheel. So being pure drag the most positive caster you can get helps improves directional stability in a straight line.

 

the tires ran on the car limit the caster that can be run as well. I have about a 1/4" clearance on turns to the fender, thats why i was wondering about the strut plate.

 

Yeah big rim and tire combo does that, mainly over 16 inch. If you dont want to go camber- caster plates then you might be SOL. Anyway, you have 5 degrees caster already which is good even it up side to side and your set. GL @ the strip.

 

The strut top setting numbers are not absolute (total) camber, they are relative to the factory preset.

In other words, you can leave them at the default 0/0, or you can get about a half a degree positive of one, the other, or both.

You could always invest in a set of adjustible camber plates.