Bernice said:
The World: "So basically, the card depicts heaven."
World = Heaven.
How can we use 'heaven' as a Significator (or co-sig) ?
If you want to leave the World in, then you have to take another card out, as there are only 21 spaces. I would take the fool out, as it is distinguished from the others by the fact it is unnumbered and by a difference in function.
But I hate to leave the fool out of play
As the fool can be played instead of any other card, he could be a significator in all questions, so all you have then is to choose one card as significator of the question. The question then is how to place the fool. One method for example would be to add up the numbers on the four corner cards, keep deducting 20 until you get a number of 21 or under, and place the fool as significator in that position. (Or you could deduct 21 until you get a number under 21, but if the four corners add up to 21, the answer would be nought, which means the fool, one of the significators could not be placed, which means the question would be void).
Or, the center card could always be co-significator, whichever card it is, and the relationship of the fools position to that decides the question...
... but perhaps that is 'streamlining' the method too far, and leading us OT and out of the interesting discussion of which cards would signify what.