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

# import sys
# sys.stdin = open('in.txt')
for _ in range(int(input())):
    c = int(input())
    a = list(map(int, input().split()))
    if a.index(max(a)) != 0:
        print(a.index(max(a)) + 1)
    else:
        for i in range(len(a) - 1):
            if a[i] > a[i+1]:
                print(i + 1)
                c = 0
                break
        if c != 0:
            print(-1)

