I believe the strongest justification for a correlation that puts LeMat between XX and XXI (didn't someone state this already, based on the 20 + 2 thing?) is that on the Day of Judgment (trump XX) the choice for each soul is between New Jerusalem (trump XXI) and oblivion (LeMat).
Levi wrote c. 1856, the 3 Minchiate Francesi versions were made somehow between 1660-1730.
In version 2 of the Minchiate Francesi (with 42 units) the Fool Momus got the position 29. As the positions 31-42 got zodiac and months function, they somehow stand outside the usual row and the used system so has (somehow) only 30 units. 29 would be the "second last" position ... as by Levi, but between Love (28) and Fortune (30).
I only have few pictures of version 2, but they should be similar to those of version 3 (where they have other numbers). There they look this way:
see more:
http://tarotforum.net/showthread.php?p=3027404#post3027404
So we have the phenomenon, that Levi made something, which in a similar way was already done before.
*********************
In the common Tarocchi game rules we have (usually), that highest trump (World), lowest trump (Bateleur) and Fool (cannot trump, but can't be captured) and all 4 kings have 4 or 5 points (the highest values in the game).
The Kings-point are not sure; Kings can be captured by each trump.
The Bateleur points are not sure; the Bateleur can be captured by each other trump.
The Fool-points are sure; but the Fool cannot capture any other card (which would increase his automatic point value)
The World-points are sure and to this one may add the points, which the player gets when he capture other cards.
So we have a natural game ranking:
highest card: World
second highest card: Fool
It really doesn't need a high philosophical explanation.