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 _ in range(t):
    n = int(input())
    li = list(map(int,input().split()))
    if len(set(li))==1:
        print(-1)
    else:
        x = max(li)
        li.insert(0,x)
        li.append(x)
        #print(li)
        for i in range(1,n+1):
            if li[i-1]==x and li[i+1]!=x and li[i]==x:
                print(i)
                break
            if li[i-1]!=x and li[i+1]==x and li[i]==x:
                print(i)
                break
            if li[i-1]!=x and li[i+1]!=x and li[i]==x:
                print(i)
                break