Just keep in mind that your total value for the cell size and border size is in pixels... a cell size of 20 means it will look for gaps at least 20 px in size... and the cell border will add to the overall size (keeping that distance away from walls/solids)
I suggest keeping the border size smaller (only 2 or 3 pixels) just to keep enemies from "Scrubbing" against walls... but a cell size of around 20 should be fine.
If you make your doorways and corridors around 30px wide or more with these parameters, you shouldn't have too many issues. Also keep the path re-evaluation time lower, that will help with over-all performance. You can even combine path finding with normal "is with range" of the player style AI - so if the enemy is within X pixels of the player they will not use path-finding any more, but rather rely on direct line of attack.
If you make your doorways even larger, use a larger cell size - it will be faster. Just remember that it's bascially cell size + border for the minimum gap. You willwant at least a few pixels in "grace" so the pathfinder can work a little easier. I always allows like 10-15% extra space at least
~Sol