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())
    pirahnas = [int(x) for x in input().split()]
    s = set(pirahnas)
    if len(s) == 1:
        print(-1)
    else:
        biggest = max(pirahnas)
        for i,p in enumerate(pirahnas):
            if p == biggest and ((i != 0 and p > pirahnas[i-1]) or (i != len(pirahnas)-1 and p > pirahnas[i+1])):
                print(i+1)
                break
