1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

def solve(arr):
    if arr.count(arr[0]) == len(arr):
        print("-1")
    else:
        mx = max(arr)
        for i in range(len(arr)):   
            if arr[i] == mx:
                if i != 0 and i != len(arr) - 1:
                    if arr[i+1] < arr[i] or arr[i-1] < arr[i]:
                        print(i + 1)
                        break
                elif i == 0:
                    if arr[i+1] < arr[i]:
                        print(i + 1)
                        break
                else:
                    if arr[i-1] < arr[i]:
                        print(i + 1)
                        break
    
    
    
i = int(input())

for j in range(i):
    k = int(input())
    m = input().split(" ")
    arr = list(map(int, m))
    
    solve(arr)