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():
    n = int(input())
    l = list(map(int, input().split()))
    m = max(l)
    for i in range(n):
        if l[i]==m:
            if i == 0:
                if l[i] > l[i + 1]:
                    print(i + 1)
                    return
            elif i == (n - 1):
                if l[i] > l[i - 1]:
                    print(i + 1)
                    return
            else:
                if l[i] > l[i - 1]:
                    print(i + 1)
                    return
                elif l[i] > l[i + 1]:
                    print(i + 1)
                    return

    print(-1)

for t in range(int(input())):
    solve()
    #print()
