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

from sys import stdin, stdout
#stdin = open('Dominant Piranha.txt', 'r') 
def II(): return int(stdin.readline())
def LI(): return list(map(int, stdin.readline().split()))
            
def solve():
    n=II()
    a=LI()
    maxa=max(a)
    imax=[i for i in range(n) if a[i]==maxa]
    ans=-1
    for i in imax:
        if i==0 and a[1]<maxa:
            ans=i+1
        elif i==n-1 and a[n-2]<maxa:
            ans=i+1
        elif i>0 and i<n-1 and (a[i-1]<maxa or a[i+1]<maxa):
            ans=i+1
        if ans>0:
            break
    stdout.write(str(ans)+"\n")

t=II()
for _ in range(t):
    solve()