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

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