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())
    set1=set(arr)
    if len(set1) == 1:
        print("-1")
        continue
        
    maxa=max(arr)
    for i in range(n):
        if arr[i] == maxa:
            try:
                if arr[i-1] < maxa:
                    print(i+1)
                    break
            except:
                try:
                    if arr[i+1] < maxa:
                        print(i+1)
                        break
                except:
                    pass
        
    
    
    
    