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 T in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    high=max(a)
    flag=True
    for i in range(n):
        if((i!=(n-1) and (a[i]==high and a[i+1]!=high)) or (i!=0 and (a[i]==high and a[i-1]!=high))):
            flag=False
            print(i+1)
            break
        
    if(flag):
        print(-1)
                
        
    
    
