Understanding GNSS Accuracy in Sony Spresense

After correcting Sony Spresens' Arduino sample = gnss.ino, storing the location measurement results in SDcard, and plotting the latitude and longitude to QGIS, I feel that the location accuracy is not as good as I expected in the following situations.

1. Changed to use QZSS_L1S.
　　static enum ParamSatType=eSatGpsQz1cQz1S;
2. Do not retrieve data from pdop>5 or higher.

1. Measure in a square where there is no shield.
2. Place the spresens on the stand for continuous measurement.

1. The pdop of the measurement results is almost 2 or less.
2. The number of satellites used for position calculation is 10-12
3. Plot results are distributed in the following ranges:
　　　Latitude direction: 33.123245239 to 33.123268127 (difference: approximately 0.082 seconds)
　　　Longitudinal direction: 131.810440063 to 131.810516357 (difference: approximately 0.274 seconds)
4. Suppose 1 second is 30 m
Direction of latitude:
distributed in a range of 2.5 m Longitudinal direction:
distributed in the range of 8.2 m 5.Attached is the plot result.
Red is the position measured by iPhone XR at the same time.
　Green is the location of the Spresens.The number is the value of pdop.