First things first, the crack will be moving around with the seasons. it will get wider and will shrink. Ceramic tile will not budge a bit. the slightest movement of the concrete will crack the tile especially along its weakest link, the grout line.
I would suggest, not knowing anything about this membrane, is to fill the crack with latex or vinyl concrete patch. this stuff does give and will have some elasticity. You apply it just like thinset or mortar.
Now, on your membrane, I am definately with you, 6 inches is NOT enough. If you do use this, then I would get another 8 foot strip and then position the 1 foot wide membrane straddled down the middle of the crack line.
JB, you are a regular on this site and IF I were you, I would wait around for others to add their two cents concerning this membrane.
I will tell you that I have definately put ceramic tile over a concrete crack filled with vinyl concrete and it has worked or the customer has not complained to me yet. In Texas, our soils fluctuate soo much and as our foundations. This was a slab foundation.