- Make the array 'outside the group' and then Add it to the Group. This requires you to Finish Group, make Array, Edit Group, Add... etc
- You could use a line based Component as an array 'guide' to provide you with the intervals you need, and then Copy Multiple. If you are in a Detail Group, use a Detail Component, if you are in a Model Group, use a Generic Model.
Here are some links to download my array guide components
These components have two instance properties - one to control the size of the 'tick', and one to control how many elements / divisions are in the array.
Download example Detail Component here
Download example Generic Model here