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


t = int(input())

for _ in range(t):
    n = int(input())
    parahnas = list(map(int, input().split()))
    indexes = []
    maxi = max(parahnas)
    # print(maxi)
    for i in range(len(parahnas)):
        if parahnas[i] == maxi:
            indexes.append(i)
    # print(indexes)
    flag = False
    for ind in indexes:
        # print(ind, end=" ")
        if (ind + 1) < (n-1) and (ind - 1) > -1:
            if (parahnas[ind+1] < parahnas[ind]) or (parahnas[ind-1] < parahnas[ind]):
                print(ind+1)
                flag = True
                break
        elif ind+1 > n-1:
            if parahnas[ind-1] < parahnas[ind]:
                print(ind+1)
                flag = True
                break
        elif ind - 1 <= -1:
            if parahnas[ind+1] < parahnas[ind]:
                flag = True
                print(ind+1)
                break

    if not flag:
        print(-1)