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

def solve():
    n = int(input())
    a = [int(x) for x in input().split()]
    mx = -1
    ind = -1
    for i in range(0,n):
        mx = max(mx , a[i])
    for i in range(0,n):
        if(a[i] == mx):
            if(i > 0 and a[i - 1] != mx): ind = i + 1
            if(i < n - 1 and a[i + 1] != mx): ind = i + 1
    if ind == -1 : print(-1,"\n")
    else: print(ind,"\n")
test = int(input())
while test > 0:
    solve()
    test -= 1