LMI also sells some of the Courtnall plans but not the Santos.
The side showing lower in the lower bout is because of the doming of the top. Whereas alot of classical builders have rims that are flat but will but have the doming of the top in the lower bout, that plan shows what the result is when the entire top is domed via a sanding dish as Steel string builders do.
This kind of makes sense since the setup and action on a Flamenco is closer to the string height on a steel string. The lowering of the sides in the lowert bout would serve to lower the height of the bridge and hence lower action.
I have built from all of the plans mentioned above. For the most part I ended up sticking closer to the Santos plan as it is very well discussed in the Courtnall book.
The Barbero plans are very good but use a bracing pattern that is not what I would usually use. It has 5 fan braces in the middle with very little angle and two longer bottom braces outside of the 5 angled like bottom braces but only crossing (reinforcing) the outer two braces. I have no problem with this but done see it as any advantage over using 7 fan braces and just not having any bottom cross braces as Santos did.
By the way...I tried something cool on my last Flamenco...Have you seen or tried "Pegheds"?
http://www.pegheds.com
It is a planetary gear INSIDE a normal looking tuning peg!! It gives a no slip solution for a Flamenco while being undetectable.
They are really slick and a good selling point that once a flamenco player sees is sold on. They are $120 a set but I would rather supply them as standard on my Flamenco than get calls from players who only sometimes play flamenco asking how to deal with slipping or sticking tuning pegs. I dont mind the price for the Peghed tuners as it is still in the same range I would allocate for good tuners on a classical.