Entrance exam cutoff calculation

#1
Last month I appeared for the phase II of a nationalized bank exam. I would like to know the effect of sample size on the cutoff score.

Unlike Phase II, candidates required for Phase III are same for both years.
Phase I exam is easier than Phase II.
Assume the difficulty level in each phase for both years to be same.( 2017 Phase I=2018 Phase I)
Also the intelligence level of students appearing in both years is same.

number of candidates appearing in each phase:
Year : Phase I > Phase II > Phase III
2017: 1250000 > 46000 > 6300
2018: 1250000 > 21500 > 6300

cut off Percentile Phase I
2017 : 46000/1250000 = 96.32 (Marks: 51.50)
2018 : 21500/1250000 = 98.28 (Marks: 56.75)

cutoff Marks
2017 : 51.50 > 50 > 45
2018 : 56.75 > result awaited > to be conducted

If in 2017,out of 46000 candidates, the 6300th candidate scored 50 marks
then in 2018, out of 21500 candidates, what should be the approx score of 6300th candidate?
Does the sample size affect the cutoff score?
Please comment on this scenario.