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

MOD = 1000000007
ii = lambda :  int(input())
si = lambda :  input()
dgl = lambda : list(map(int, input()))
f = lambda :   map(int, input().split())
il = lambda :  list(map(int, input().split()))
ls = lambda :  list(input())
from collections import *
for _ in range(ii()):
    n=ii()
    a=il()
    v=-MOD
    for i in range(0,n):
        if(a[i]>v):
            if(i>0 and a[i-1]<a[i]):
                ans=i
                v=a[i]
            elif(i < n-1 and a[i+1]<a[i]):
                ans=i
                v=a[i]
    if(len(set(a))==1):
        print(-1)
    else:
        print(ans+1)