Max heap and array relation
Suppose an array $A$ is a maxheap.  Inserting a large element in the first position of $A$ does not necessarily preserve the maxheap property.  The maxheap property requires a node's value to be larger than both its children's values, for each node in the tree.  If the value inserted in the first position is larger than all values in the array, then the maxheap property is preserved at the root node, but might not be preserved at some of the other (lower level) nodes. 

We can construct an initial array $A$ such that the nodes in the subtree rooted at the right child of the root have much larger values than the nodes in the subtree rooted at the left child of the root. When a new value is inserted in the first position of the array, the tree changes so that the smaller values in the left subtree become parents of the larger values in the right subtree, causing the maxheap property to be violated. For example, take $A=[6,3,5,2,1,4]$, which is a maxheap.  Inserting a $7$ in the beginning modifies $A$ to $A=[7,6,3,5,2,1,4]$, which is not a maxheap because the node with value $3$ is a parent of the node with value $4$.