"Your results are back: it's negative"......um, is that a bad thing?
Jatta Pake wrote:
Max of 4 Army units per land space. City size is irrelevant to the stacking rule.
"Army Stacking Limit
You may never have more than 4 Army units in the same Land space (Army units on Ships do not have a stacking limit but are limited to two per Ship)." Rules Page 9.
This. Although there is a Persian leader in the civilizations expansion that allows his army to be five figures.
I wonder if the OP confused this rule with the one about how the size of the city dictates how many units one can build in that city...