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())
    a = list(map(int,input().split()))
    mx = max(a)
    if(a.count(mx) == n):
        ans = -1
    else:
        flag = 0
        for i in range(n):            
            if(a[i] == mx):
                if(i < n-1 and a[i+1] != mx):
                    ans = i+1
                    flag = 1
                elif(i > 0 and a[i-1] != mx):
                    ans = i+1
                    flag = 1
            if(flag):
                break
            
    print(ans)
