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 _ in range(int(input())):
    n=int(input())
    a=[int(i) for i in input().split()]
    m=max(a)
    if(a.count(m)==n):
        print(-1)
        continue
    ans=[]
    for i in range(n):
        if(a[i]==m):
            ans.append(i)
    x=0
    for i in ans:
        if(i+1<n and a[i]>a[i+1]) or (i-1>=0 and  a[i]>a[i-1]):
            x=i+1
            break
    print(x)
        
