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())):
    n = int(input())
    l = list(map(int,input().split()))
    if len(set(l)) == 1:
        print(-1)
        continue
    x = max(l)
    f=0
    for i in range(1,n-1):
        if l[i] == x and l[i - 1] < x:
            print(i + 1)
            f=1
            break
        elif l[i] == x and l[i + 1] < x:
            print(i + 1)
            f=1
            break
    if f==0 and l[0] == x and l[1] < x:
        print(1)
    elif f == 0 and l[n-1] == x and l[n-2] < x:
        print(n)
    elif f == 0:
        print(-1)