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 solution():
    #here you start coding!
    n = int(input())
    a = list(map(int, input().split()))
    que = []
    for i, v in enumerate(a):
        que.append((v, i+1))
    que.sort()
    if que[0][0] == que[-1][0]:
        print(-1)
        return
    else:
        maxvalue = que[-1][0]
    for i in range(n):
        if a[i] == maxvalue:
            if i-1 >= 0 and a[i-1] < maxvalue:
                print(i+1)
                return
            if i+1 < n and a[i+1] < maxvalue:
                print(i+1)
                return


def main():
    testcase = int(input())
    for i in range(testcase):
        solution()
    return


if __name__ == "__main__":
    main()

