i'd have suggested that individual grass would still point upwards, not perpendicularily to the ground they're growing on... even if the neighbouring "thread of grass" starts lower or higher than "your own grass", just like trees would grow upward regardless of the slope they're on.
Having the grass growing at 45° somehow gives the feeling that you picked a chunk of ground that was initially horizontal and tilted it to 45° without leaving time for the grass to adapt to its new condition. And even in that case, it would rather "bend towards the ground" (as you would draw it at the border of a cliff) because its roots wasn't ready to make it stick straight in those conditions.
