By no means am I proclaiming myself an expert, but I have seen it discussed that Alli does well when he's running into the box (like Lampard) to get on the end of some cut-backs.
Those two goals from Alderweireld crosses also seemed to come from a penetrating run that the defenders couldn't deal with.
I think the other thing is that Alli can probably have a greater impact by playing in midfield and seeing more of the ball. Would possibly be easier to mark him out of the game if he was played as a forward too, not least because of his slight frame (Kane has only really become a force since he bulked up).
TL;DR - keep him in midfield.