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 math import *
from sys import *
t=int(stdin.readline())
for _ in range(t):
    n = int(stdin.readline())
    a = list(map(int, stdin.readline().split()))
    b=a.copy()
    f=0
    for i in range(1,n):
        if a[i]!=a[i-1]:
            f=1
            break
    if f==0:
        print(-1)
    else:
        x=max(a)
        for i in range(n):
            if a[i]==x:
                if i-1>=0:
                    if a[i-1]<x:
                        j=i+1
                        break
                if i+1<n:
                    if a[i+1]<a[i]:
                        j=i+1
                        break
        print(j)