If we measure the gap between abdominals it is recommended that we do it in horizontal position, with our head raised. More accurate result can be achieved if we retract our belly as much as we can.
Initially, if one cannot retract their belly at all, the result will be a wider gap, then later with retracting the belly, this number will be less.
It can happen that, for the first time, we measure for example a 4 finger wide gap without being able to retract the belly. After a few weeks of practice, when we learned to retract our belly, the gap will be smaller. This is because the trapdoor effect. (Trapdoor effect: If you don’t stretch your abdominals when you do something physically demanding the increased pressure in your belly will push the entrails outwards, which push open the straight abdominals like a trapdoor, further elongating the sinewy plate.)
The measurement should happen with retracted belly if possible.