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())
    arr=list(map(int,input().split()))
    a=max(arr)
    b=min(arr)
    if a==b:
        print(-1)
    else:
        ans=-1
        for i in range(n):
            if i==0 and arr[i]==a:
                if arr[i+1]!=a:
                    ans=i+1
                    break
            elif i==n-1 and arr[i]==a:
                if arr[i-1]!=a:
                    ans=i+1
                    break
            else:
                if arr[i]==a and (arr[i-1]!=a or arr[i+1]!=a):
                    ans=i+1
                    break
        print(ans)