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())
    arr=list(map(int,input().split()))
    k=max(arr)
    if arr.count(k)!=n:
        ans=-1
        for i in range(n-1):
            if arr[i]==k and arr[i+1]!=k:
                ans=i+1
                break
            elif arr[i]!=k and arr[i+1]==k:
                ans=i+2
        
            
        
        print(ans)
    else:
        print("-1")
    

     
     