No, it should be $count % 2 == 0, rather than $count % 2 > 0. The > 0 was superflous to begin with.
% is (more or less) the remainder on integer division. So, you have $count, which is integers, 1 .. N. 1 % 2 === 1, 2 % 2 === 0, 3 % 2 === 1, 4 % 2 === 0 etc.
Since the only value present > 0 is 1, and the only value not > 0 is 0, you get boolean true on 1 and boolean false on 0. But 0 allready casts to boolean false, and non-zero integers allready cast to boolean true. Therefor, > 0 was superflous since it doesn't change anything from having just if ($count % 2).
So, if you had a $count value of 1, 3, 5 etc, you'd get 'grid end', and on 2, 4, 6 etc you'd get 'grid'. But, since this code part would not execute for $count == 1 (which gave 'full featured' instead), you'd actually only get 'grid end' on 3, 5 etc.
So, in all, your code gave you:
'full featured' for 1st post.
'grid' for 2nd'
'grid end' for 3rd
'grid' for 4th
'grid end' for 5th
etc.
Since you now want to move the 1st post "into the grid", you can no longer issue grid end on uneven posts counts since that would give you one post on the first grid line, 2 on the second etc, and the only difference from before being that the initial post wasn't using the full page width, but rather just half of it. And, to change from uneven to even posts, you need to make % 2 be true when the remainder is 0, rather than false, hence == 0
if ($count % 2 == 0) gives
1 % 2 == 0 => 1 == 0 => false
2 % 2 == 0 => 0 == 0 => true
etc