There are two versions of the FoilMount 2.0; the standard FoilMount and the ridge FoilMount. The difference is a groove cut out lengthwise on the bottom of the ridge FoilMount (figure 1 below). 
Figure 1 Standard versus Ridge FoilMount
This groove allows the ridge version to bend in the middle between the tracks to allow for a "ridge", "vee" or very slight double or single concave 1-2mm max. Not only does this groove allow the FoilMount ridge version to bend slightly it also will absorb the top of a sharp ridge or prominence on the bottom of the board making the surface more flat for installation (figure 2 below). 
Figure 2 Ridge FoilMount for Prominence or Spine
Both versions of the FoilMount need to be mounted in an area that is flat with only a slight ridge or curve when using the ridge mount. The reason for this is the FoilMount itself is flat, but more importantly the base plate for your hydrofoil is flat! So if you try to mount your hydrofoil base plate to a surface that is not flat it will either rock side to side or front to back or you tighten the attachment bolts to either break your mount, base plate, or board. What is a lot of curve, rocker, etc? Well, lets define a few terms first.
Tail Rocker (figure 3) - This is the upward or downward curve of a board toward the aft end, it is usually upward and almost always greater toward the tail
Figure 3 Tail Rocker
Single Concave - This is an inwardly (toward the inside of the board) singularly curved surface.
Double Concave - This is an inwardly (toward the inside of the board) double curved surface with a spine or ridge in the middle
Belly - This is the opposite of single concave with the curved surface extruding out of the board...like a Santa's belly.
Vee or Ridge - This is two flat walls that meet in the middle to make a ridge line...similar to double concave but both sides are more flat and less curved.
Flat - Exactly what the name implies, the bottom is flat except for a slight curve on the sides to fair into the rail of the board.
Spine - This is a ridge line that runs down the board. It usually has an area that is slightly curved next to it but isn't associated with a double concave or ridge shape.
Figure 4 Board Contour Shapes
When to use which version of the FoilMount
Standard
The standard mount is good for most boards as most boards actually have a flat area in the mounting location. The area that needs to be flat should measure 14" long (tip to tail) and 10" wide (side to side). The exact size of the FoilMount is 13.5" long by 9.5" wide. Many boards with a large single concave are actually flat in the middle and only have slight curves on the outside. The best way to tell is to dry-fit your FoilMount in the prospective mounting location before install. When you do this, make sure all sides and corners are touching the board with no more than pinkie finger pressure.
Ridge
The ridge mount is a great way to accommodate boards with a very slight amount of concave, ridge, vee, or a slight spine or prominence. Just make sure that the measurement of the concave, ridge, or vee isn't more than 1-2mm as measured in the method in figure 5 below. Also, there can be NO curve on the sides of the vee, ridge, or concave on either side of the groove so that both sides of the ridge FoilMount are completely touching the board. See figure 2 above for install over a slight spine or prominence. The ridge FoilMount is not suitable for a belly bottom shape. It is also not suitable for any bottom geometry where on a dry-fit the entire surface of the mount isn't touching the board with only pinkie pressure. The ridge FoilMount cannot be used if the angle is too severe as it will cause board or base plate damage. When dry-fitting a ridge FoilMount an acceptable angle can be approximated using the technique in figure 5 below and ensuring no more than 1mm or maximum 2mm spacing off the board. 
Figure 5 How to Measure for Ridge Mount
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