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 collections import Counter
from collections import OrderedDict
from collections import defaultdict 
import bisect
def freq_count(mylist):
    return Counter(mylist)
t=int(input())
for _ in range(t):
    n=int(input())
    #l,r=map(int,input().split())
    arr=[int(x) for x in input().split()]
    #grid=[[int(x) for x in input().split()] for x in range(n)]
    #arr=list(input())
    maxa=max(arr)
    for i in range(n):
        if i ==0:
            if arr[i] == maxa and arr[i] > arr[i+1]:
                print(i+1)
                break
        elif i == n-1:
            if arr[i] == maxa and arr[i]> arr[i-1]:
                print(i+1)
                break
        else:
            if arr[i]== maxa:
                if arr[i] > arr[i-1] or arr[i] > arr[i+1]:
                    print(i+1)
                    break
    else:
        print("-1")
    
    
    
    
    