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

for _ in range(int(input())):
    am = int(input())
    arr = list(map(int,input().split()))
    m = max(arr)
    fl = False
    ans = 0
    for i in range(am):
        if arr[i] == m:
            if i == 0:
                if arr[i+1] < arr[i]:
                    fl = True
                    ans = i
                    break
            elif i == am-1:
                if arr[i-1] < arr[i]:
                    fl = True
                    ans = i
                    break
            else:
                if arr[i-1] < arr[i] or arr[i] > arr[i+1]:
                    fl = True
                    ans = i
                    break
    if fl:
        print(ans+1)
    else:
        print(-1)
