Iterator Size for C++ STL Array

I was trying to understanding STL arrays on a surface level and wrote some code. It goes like this -

#include <iostream>
#include <array>
#include <algorithm>

using namespace std;

int main()
{
    const int p = 8;
    array<int, p> arr;

    for(int i=0; i<p; i++) 
        cin >> arr[i];

    array<int, 1>::iterator at, bt; // this line is the main focus

    at = arr.begin();
    bt = arr.end();

    sort(at, bt);

    for(at = arr.begin(); at != arr.end(); at++)
        cout << *at << endl;

    return 0;
}

In the line array<int, 1>::iterator at, bt;, I defined the iterator to be specific to the size of the array with 1 element. Yet it works perfectly for sizes which are not equal to 1 (8 in this case). The sorting and the print for-loop both work fine.

I changed the 1 in the line to something random, like array<int, 183>::iterator at, bt;, and it still works. What's surprising was when I changed the size to a negative number (let's say -90) or 0, it also seems to work perfectly fine.

I initialized variable at with arr.begin(). How is it possible for an iterator of type array<int, 1> be assigned to array<int, 8>.

What could be the reason for this? What is the underlying concept of defining a size for STL Array Iterators?