What you normally get when you insert a table (whether you are using an IF field or not) is a paragraph mark
before the table. When your IF field is the only thing in a paragraph, the paragraph mark you see below the table is just that paragraph mark, not something inserted by the field.
So if for example you want to put some text on the line immediately below the table, you can use
{if <mergefield>="ABC""I am inserting table""N/A"}the text you want
Just guessing here, but if what you want is to follow the table inserted by the IF field with another table in such a way that they look
like a single table, the problem is not the paragraph mark after the first table, it's the paragraph mark
before the second table. In that case you may be able to eliminate the gap by selecting the paragraph mark before the second table and setting its font to Hidden.
Peter Jamieson