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())):
    m=int(input())
    a=list(map(int,input().split(' ')))
    if max(a)==sum(a)/m:
        print(-1)
    elif a.count(max(a))==1:
        print(a.index(max(a))+1)
    else:
        for i in range(m-1):
            if a[i]>a[i+1] and a[i]==max(a):
                print(i+1)
                break
            elif a[i]<a[i+1] and a[i+1]==max(a):
                print(i+1)
            else:
                continue
    
