To begin, I created 2 grids.  One with U and V length of 2 and 2, subdivisions were also 2 and 2, the other grid, with the U and V length of 32 and 32, subdivision of U and V was also 32 and 32. 
Freeze it

Keeping the units the same size means the lower and upper grid points are the same size, and will match up, which will help you achieve a good result.  The example I created here is a little small for this.  To get better results you may need a larger grid and more pins, but at the cost of longer render times.

It’s a good idea to freeze every step of the way with this tutorial as scenes will be heavy.