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