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

from queue import Queue

t = int(input())
for _ in range(t):
    kek = int(input())
    piras = list(map(int, input().split()))
    if len(set(piras)) <= 1:
        print("-1")
        continue
    jo = max(piras)
    end = None
    for indx, pira in enumerate(piras):
        if pira == jo:
            if indx - 1 >= 0 and piras[indx - 1] < pira:
                end = indx
                break
            if indx + 1 < len(piras) and piras[indx + 1] < pira:
                end = indx
                break
    print(indx+1)


