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 collections import Counter
for _ in range(int(input())):
    n = int(input())
    lst = list(map(int, input().split()))
    ans = -1
    m = max(lst)
    for i in range(n):
    	if lst[i]==m:
    		if i!=0 and lst[i-1]<lst[i]:
    			ans=i+1
    			break
    		if i!=n-1 and lst[i+1]<lst[i]:
    			ans=i+1
    			break
    print(ans)
    			