Can't get Beersmith to convert AG to PM accurately...

I downloaded Beersmith with the intention of converting AG batches to partial mashes, since I will be doing partial mashes from now on. I put in an AG recipe from "How to Brew" that had the partial mash instructions included. I put in the AG recipe exactly as the book listed, but for some reason I kept getting a different OG, FG, and bitterness level. Also, the conversion to PM yielded a very different recipe.

What could I be doing wrong? I kept having trouble with boil volume. Do I keep the batch size at 5 gallons, even though most recipes give a 6.5 pre boil gravity and a 5.5 OG?

make sure the efficiencies for the recipes are the same.

I don't really like the automatic conversion in Beer Smith I feel like it creates weird ratios and tries to match the color too exact. I also find that it's pretty easy to do it by hand. Here are the steps I take.

1. Make sure all your PM equipment is setup correctly in Beer Smith.
2. Start a new recipe, set it to your PM equipment and the type to Partial Mash.
3. Take all the specialty grains from the AG and add it to your new PM recipe.
4. Add base malt until you reach the limit of your equipment.
5. Add extra light DME or LME until you get to the OG of the AG recipe.
6. Add hops to hit the IBU of the AG recipe.
7. Enjoy your new PM recipe!