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())
    *a,=map(int, input().split())
    if len(set(a))==1:
        print(-1)
        continue
    mx=max(a)
    fin=False
    for i in range(n):
        if a[i]==mx:
            if i and a[i-1]<a[i]:
                print(i+1)
                fin=True
                break
            if i<n-1 and a[i]>a[i+1]:
                print(i+1)
                fin=True
                break
        if fin:
            break
