HI Jill,
Welcome aboard! It has been well documented that you need to account for the thickness of the paper when focusing on the printing easel. The depth of field is not very good on enlarging lens and even stopped down there is some error. So, since I use several different papers and I just keep a wasted piece (marked with the name of the paper) of each paper I use near the enlarger column. I just place the paper on the easel and mt focus tool on the paper and then I just focus my little heart out.