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 ii in range(t):
    n=int(input())
    a=[int(i) for i in input().split()]
    for i in range(n):
        if a[i]!=a[0]:break
        if i==n-1:
            print(-1)
            continue
    k=max(a)
    if a[0]>a[1] and a[0]==k:
        print(1)
        continue
    if a[n-1]>a[n-2] and a[n-1]==k:
        print(n)
        continue
    for i in range(1,n-1):
        if a[i]==k:
            if a[i]>a[i-1] or a[i]>a[i+1]:
                print(i+1)
                break