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

for i in range(int(input())):
    x = int(input())
    a = list(map(int, input().split()))
    if len(set(a)) == 1:
        print(-1)
    else:
        r = max(a)
        ans = -1
        for j in range(x - 1):
            if a[j] == r:
                if a[j + 1] < r:
                    ans = j + 1
                    break
                if j>0:
                    if a[j-1]<a[j]:
                        ans=j+1
                        break
        if ans == -1:
            ans = x
        print(ans)
