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

# cook your dish here
for _ in range(int(input())):
    n=int(input())
    a = [int(x) for x in input().split()]
    u=max(a)
    x=0
    for i in range(n):
        if a[i]==u:
            if  i!=n-1 and a[i+1]<a[i]:
                x=1
                print(i+1)
                break
            if a[i-1]<a[i] and i!=0:
                x=1
                print(i+1)
                break 
            
    if x==0:
        print(-1)