??curve offset from grid question??

Hi,
I have encountered a problem for a long time.
I create a diamond grid, base on cut a rec grid in half and distort it.
then I offset the cell curve. it seems no problem when the offset is small. but as long as it gets bigger, the shape seems lost it coordinate.

basically, if the new shape is less than 33% of original scale, the problem comes.

anyone knows the trick?