how to tell what Planet Size you will get?

these are the average planet sizes
position 1: average: 64, 60% from 48 to 80 fields
position 2: average: 68, 60% from 53 to 83 fields
position 3: average: 73, 60% from 54 to 82 fields
position 4: average: 173, 60% from 108 to 238 fields
position 5: average: 167, 60% from 95 to 239 fields
position 6: average: 155, 60% from 82 to 228 fields
position 7: average: 144, 60% from 116 to 173 fields
position 8: average: 150, 60% from 123 to 177 fields
position 9: average: 159, 60% from 129 to 188 fields
position 10: average: 101, 60% from 79 to 122 fields
position 11: average: 98, 60% from to 116 fields
position 12: average: 105, 60% from to 129 pfields
position 13: average: 110, 60% from 60 to 160 fields
position 14: average: 84, 60% from 42 to 126 fields
position 15: average: 101, 60% from 54 to 149 fields

It is better to colonize 4, 5 ,6 slots as they give the most fields.