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 _ in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    b=max(a)
    for i in range(n):
        if a[i]==b:
            j=i
            break
    y=-2
    for i in range(j,n):
        if i==0:
            if a[i]>a[i+1]:
                y=i
                break
        elif i==n-1:
            if a[i]>a[i-1]:
                y=i
                break
        else:
            if a[i]>a[i-1] or a[i]>a[i+1]:
                y=i
                break
    print(y+1)