In general, one of the most common learning mistakes of either straddle or inside endo to full pirouette is to swing down crooked after the pirouette. The reason for this mistake is an excess of support transfer to the post arm. The gymnasts shift their weight like they were going to perform the regular front pirouette that they have learned before, and that really requires a support transfer beyond the vertical of the post arm to finish square in a different bar position.
Technically correct front pirouettes on the horizontal bar or the uneven bars must be completed by the vertical or even slightly before. Kicking up with an undergrip short of reaching a complete vertical handstand performing a front pirouette and falling over flat in overgrip lend the athlete valuable understanding and experience about how to begin an early pirouette ahead of the body reaching the vertical line.
Low single rail full pirouette drills can be trained to a mixed-grip first, and then to a complete eagle grip. Some of the goals are to keep the body fully stretched during the turn without any arch or pike, and when coming down, to land straight on the soft mat instead of crooked to either the left or right side of a perfect perpendicular line in relation to the rail.