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

def eatReturn(index, myList):
    if index > 0 and myList[index] > myList[index - 1]:
        return True
    elif index < len(myList) - 1 and myList[index] > myList[index + 1]:
        return True
    return False
    
t = int(input())
for i in range(t):
    size = int(input())
    createdList = input().split()
    dominate = False
    for i in range(size):
        createdList[i] = int(createdList[i])
    bigChungus = createdList[0]
    for i in createdList:
        if i > bigChungus:
            bigChungus = i
    for i in range(size):
        if createdList[i] == bigChungus:
            if eatReturn(i,createdList):
                print(i + 1)
                dominate = True
                break
    if not dominate:
        print(-1)