Second, I'll discuss stunts which can help an outsized team to more effectively defend the post. Finally I'll address how to handle screening actions in the paint area. Regardless of what type of defense you play, the goal of defense is to keep the ball from advancing closer to the basket at all times. Any pass that advances the ball closer to the hoop should be pressured or denied. This means for you and your smaller team, that at no times should you ever allow an uncontested pass into the post.
Pressure starts on the perimeter.
The smaller your team is the more pressure they should exert on the passer. Good post players use their body effectively to seal out a defender from a position. If there is little pressure on the ball, there is little time to react. The greater the pressure the more chance both the post defender and help defender have to recover position and either deflect or steal a pass to the post. If your team has considerable troubles in the half court post defense because of size, you better consider extending pressure and making the attacking team use more time off the shot clock in the backcourt or getting entered into their offense through full court man or zone pressure.