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

testcases = int(input())
for testcase in range(testcases):
    n = int(input())
    temparr = input()
    temparr = temparr.split()
    arr = []
    dicts = {}
    for i in temparr:
        i = int(i)
        arr.append(i)
        if i not in dicts:
            dicts[i] = 1 
    if len(dicts) == 1:
        print(-1)
        continue 
    getmax = max(arr)
    ans = 0
    for i in range(n):
        if i == 0  and arr[i] == getmax and arr[i + 1] < getmax:
            ans = i +  1 
            break 
        elif i == (n-1) and arr[i] ==getmax and arr[i - 1] < getmax:
            ans = i + 1 
            break
        elif arr[i] == getmax and (arr[i -1] < getmax or arr[i + 1] < getmax) and i != 0 and i != (n - 1):
            ans = i + 1 
            break
    
    print(ans)
    
    
    
    
    
    
        