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

t = int(input())

for ti in range(t):
    n = int(input())
    # m = li[0]
    li = [int(i) for i in input().split()]
    # for p,i in enumerate(li):

    m = max(li)
    if li.count(m) == len(li):print(-1)
    else: 
        for p,i in enumerate(li):
            if i==m:
                if p>0:
                    if li[p-1] < i:
                        print(p+1)
                        break
                if p<n-1:
                    if li[p+1] < i:
                        print(p+1)
                        break