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 i in range(int(input())):
    n = int(input())
    s = list(map(int, input().split()))
    if len(s) == s.count(s[0]):
        print(-1)
    else:
        i = s.index(max(s))
        if (i < n-1 and s[i]> s[i+1]) or (i > 0 and s[i] > s[i-1]) :
        	print(i+1)
        else:
        	while i < n-1 and s[i]==s[i+1]:
        		i = i+ 1
        	print(i+1)
