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 i in range(int(input())):
    n=int(input())
    l=[int(x) for x in input().split()]
    if len(l)==l.count(l[0]):
        print(-1)
    else:
        maxv=max(l)
        #print(maxv)
        for i in range(n):
            if l[i]==maxv:
                if i-1>=0 :
                    if l[i]>l[i-1]:
                        index=i
                if i+1<n:
                    if l[i]>l[i+1]:
                        index=i
        print(index+1)