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())
    f = list(map(int, input().split()))
    m = max(f)
    if len(set(f)) == 1:
        print(-1)
    else:
        for i in range(n):
            if f[i] != m:
                continue
            if i == 0 and f[i+1] < f[i]:
                print(i+1)
                break
            if i == n-1 and f[i-1] < f[i]:
                print(i+1)
                break
            if i > 0 and i < n-1 and f[i-1] < f[i] or f[i+1] < f[i]:
                print(i+1)
                break 