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

t = int(input())
for iii in range(t):
    n = int(input())
    a = [int(i) for i in input().split()]
    s = a[:]
    x = max(s)
    if max(a) == min(a):
        print(-1)
    else:
        for i in range(len(a)):
            if a[i] == x:
                if i == 0:
                    if a[i] > a[i + 1]:
                        print(i+1)
                        break
                elif i == len(a)-1:
                    if a[i] > a[i - 1]:
                        print(i+1)
                        break
                else:
                    if (a[i] > a[i + 1]) or (a[i] > a[i - 1]):
                        print(i+1)
                        break