Ok, so I've been brewing about 3 years now, and using Beersmith for about 2.5. As far as I can tell, I have all my numbers and settings punched in correctly. My problem is, I nearly always exceed the pre-boil gravity estimate, yet nearly always come up a bit shy on the post-boil reading. What would this imply? I always hit my water measurements/goals as well.
This equates to having a boil-off less than you have told beersmith
ie: Your true boil off is smaller than your telling the software. If your volumes are correct going into the fermentor this can still occur if you are losing volumes elsewhere.
Kettle trub
Kettle dead space
Hops absorption
Plate chiller/hoses dead space
Spillages
Gravity samples
These are all additional causes of lost volume, some large, some very small. All can contribute to overestimating your boil-off reading.
The other likely cause is inaccurate readings of pre-boil volume and pre-boil gravity.
Make sure you are measuring gravity at the correct calibration temperature and factoring in the correct shrinkage of 4% in the post-boil volume calculations (4% is set as default for post boil which is good, but 2.5% is a more useful value for calculating true mash efficiency based on preboil volumes and temperatures).
Make sure you measure kettle dead-space, hop absorption and kettle trub to come up with a fixed value of trub loss and kettle dead space in beer smith. This can remain unchanged from batch to batch assuming the hop bills do not change enormously.
In short, there are quite a few possible solutions.
Post a screenshot of your equipment profile. It may highlight some causes. It takes a bit of detective work sometimes to nail down these data errors. once you get it right Beersmith is amazingly accurate.