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())
    v=[int(i) for i in input().split()]
    m=max(v)
    f=False
    for i in range(1,n):
        if v[i]==m:
            if (i==0 and v[i+1]<m) or (i==n-1 and v[i-1]<m) or 0<i<n-1 and (v[i+1]<m or v[i-1]<m):
                f=True
                m=i
                break
    print(m+1 if f else -1)
