Grosjean was causing chaos near the front in 2012. By the end of 2013 he was turning similar starting positions into regular podiums. Your claim that their starting positions have helped them out last year is totally wrong I am afraid.
I think it's slightly different for both drivers.
It hasn't helped Pastor because he never could drive on a crowded track. His whole GP2 history is one of winning feature races from the front and crashing out when the grid was reversed. Williams admit to calling him in when he was in traffic, even if it was not the ideal pit stop window. You couldn't guarantee what might happen if you left him out.
On the other hand, he wasn't much better at mid grid. In 2012, he had some 15 top ten starts and only converted three (I think, from memory) into points finishes.
'First lap nutcase' had rather different problems . . . like the start. But there's at least one race where he recovered well from a low qualifying position.