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())
    s = input().split()
    v = list(map(int, s))
    #print(v)
    mx = max(v)
    result = -2
    for i in range(n):
        if v[i] == mx:
            if i > 0 and v[i-1] < mx:
                result = i
                break
            if i < n - 1 and v[i+1] < mx:
                result = i
                break
    print(result + 1) 
        
        