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=list(map(int,input().split()))
    if max(a)==min(a):
        print(-1)
    else:
        m=max(a)
        if a[0]!= m:
            for i in range(n):
                if a[i]==m:
                    print(i+1)
                    break
        else:
            for j in range(n):
                if a[j]>a[j+1]:
                    print(j+1)
                    break
    
                
                
        