I also use sanding sealer. I use Zinsser brand and thin it about 1:1, this gives me some shellac with a lot of drier in it. Next I apply the sealer to the uncarved side and let it suck it up. This will dry fast with all the drier in it. When dry to the touch (2-3 minutes) l do the carved side, If you think about it the carving gives you a ton of end grain so sealer will be absorbed big time. There is your imbalance on both sides. Conclusion: by applying the smooth side first you are introducing the moisture to the side less likely to cup first(giving it a head start). When the sealer goes on the carved (end grain) side it will be pulling against the 1st wet side hopefully evening out the tension a bit. After the sealer is on there I let the project sit a day or two to give the solvents a chance to dissipate. l find the addition of the thinned sealer on my carving closes up the intersecting cuts nicely and makes for better results. Hope this helps.