It’s not unusual to see football shaped divits on a table top when they aren’t used correctly. If you put them to close to the surface, the biscuits will swell from the glue, making a raised area. Then, if you sand it smooth before the swelling subsides, it leave a depression shaped like the biscuit. I’m not poo-pooing biscuits, but put them at or below 1/2 way down the thickness, and then let them dry thoroughly before working your table top down.

"I long for the day when coke was a cola and a joint was a bad place to be" Merle Haggartd