Array Parametric family could not maintain constraints

[Anonymous]

Hi Gents, 

I am currently working now in creating a Manhole with step rung on it. I created a separate family for the step rung and load it in the manhole family. 
I would like to just populate the step rung using array tool with certain formula. 

I created a constraint so that it would maintain a distance from the manhole thickness even if we change the manhole size. 
The Problem I've got is after the array tool has been completed and elements have been grouped.
They are not satisfying the constraints. 

What is wrong ?????

Many Thanks!

[ToanDN · Accepted solution]

Make the initial array to create only the second instance.  Constrain the second instance  right away.  Now assign the formula to the array to populate the rest and all instances should align properly.

[Anonymous]

Thanks @ToanDN. that works well!!