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!=0:
    t-=1
    n=int(input())
    a=list(map(int,input().split()))[:n:]
    b=set(a)
    if len(b)==1:
        print("-1")
    else:
        c=max(a)
        if a[0]==c and a[1]<c:
            print("1")
        elif a[n-1]==c and a[n-2]<c:
            print(n)
        else:
            for i in range(1,len(a)-1):
                if a[i]==c and a[i+1]<c:
                    print(i+1)
                    break
                elif a[i]==c and a[i-1]<c:
                    print(i+1)
                    break
            
                