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

t=int(input())
while(t):
    n=int(input())
    l=list(map(int,input().split()))
    if(len(set(l))==1):
        print("-1")
    else:
        m=max(l)
        for i in range(len(l)):
            if(l[i]==m):
                if((i-1)>=0 and l[i-1]<l[i]):
                    print(i+1)
                    break
                if((i+1)<n and l[i+1]<l[i]):
                    print(i+1)
                    break
    t=t-1