Calculating side setting triangles for blocks on point

I volunteered today to make a donation quilt for a young girl with lymphocytic leukemia. I still have my blocks from a swap called Black Tie Affair and I'd like to use those. I plan on using 13 of the blocks with 2 inch (f) sashing with cornerstones. Every time I try to set blocks on point with sashing, my side setting triangles turn out too short and I lose the points on the sashing. What am I doing wrong in figuring those sides? The blocks of course are 12 inches (f). If the sashing is 2 inches do I calculate for a 14 inch block? I don't have much white on white left so I'm trying to be accurate.

duh...my shorthand explained

(f)=finished
(uf)=unfinished