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

n = int(input())
for i in range(n):
    count = int(input())
    sharks = [int(x) for x in input().split()]
    deltaMax = 0
    indexOfSuperShark = -1
    maxSharkWeight = max(sharks)
    for j in range(len(sharks) - 1):
        delta = abs(sharks[j] - sharks[j+1])
        if delta > deltaMax and (sharks[j] == maxSharkWeight or sharks[j+1] == maxSharkWeight):
            deltaMax = delta
            indexOfSuperShark = j + 1 if sharks[j] > sharks[j+1] else j + 2
    if indexOfSuperShark == -1:
        print(-1)
    else:
        print(indexOfSuperShark)