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 tt in range(t):
    n = int(input())
    a = list(map(int, input().split()))
    mx = max(a)
    if mx==min(a):
        print(-1)
    else:
        if a[0]==mx and a[0]>a[1]:
            print(1)
        elif a[-1]==mx and a[-2]<a[-1]:
            print(n)
        else:
            for i in range(1, n-1):
                if a[i]==mx and (a[i-1]<a[i] or a[i]>a[i+1]):
                    print(i+1)
                    break