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 dominant(piranhas):
    maximum = max(piranhas)
    for index, piranha in enumerate(piranhas):
        size = piranha
        pointer = 0
        negative = True
        positive = True
        while positive and negative:
            try:
                if positive:
                    if size > piranhas[index + 1 + pointer]:
                        size += 1
                    else:
                        positive = False
            except:
                positive = False

            if index - 1 -pointer < 0:
                negative = False

            if negative:
                if size > piranhas[index - 1 - pointer]:
                    size += 1
                else:
                    negative = False

            pointer += 1
            if size > maximum:
                return index + 1

    else:
        return -1


for x in range(int(input())):
    throw = input()
    piranhas = [*map(int, input().split(" "))]
    print(dominant(piranhas))