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()))
    b=sorted(a)
    p=b[-1]
    if b[0]==p:print(-1)
    else:
        an=0
        for i in range(n):
            if i==0:
                if a[i]==p and a[i+1]<p:
                    an=i+1
                    break
            elif i==n-1:
                if a[i-1]<p:
                    an=i+1
                    break
            elif a[i]==p:
                if a[i-1]<p or a[i+1]<p:
                    an=i+1
                    break
        print(an)
