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())
    ar=list(map(int,input().split()))
    
    if len(set(ar))==1:
        print(-1)
    else:
        maxi=max(ar)
        flag=0
        for i in range(n-1):
            if ar[i]==maxi and ar[i+1]!=maxi:
                ind=i
                flag=1
                break
        if flag!=1:
            for i in range(1,n):
                if ar[i]==maxi and ar[i-1]!=maxi:
                    ind=i
                    flag=1
                    break
        print(ind+1)