Why is the shift done by 3 elements even though BatchSize = 100?

Question

Python

Explain why when scrolling the wheel in QListWidget, the top item first becomes "item 4", then "item 7", "item 10" and so on, although BatchSize = 100? That is, BatchSize is not the number of elements when scrolling the mouse wheel? Here is the code ready to run:

import sys

from PyQt5 import QtCore, QtWidgets

app = QtWidgets.QApplication(sys.argv)
window = QtWidgets.QWidget()
window.setWindowTitle("Класс QListView")
window.resize(300, 150)
view = QtWidgets.QListView()

view.setLayoutMode(QtWidgets.QListView.Batched)
view.setBatchSize(100)

L = []
for i in range(1, 100000):
    L.append("Пункт {0}".format(i))
model = QtCore.QStringListModel(L)
view.setModel(model)
box = QtWidgets.QVBoxLayout()
box.addWidget(view)
window.setLayout(box)
window.show()
sys.exit(app.exec_())

Answer 1

Is not . BatchSize - how much is rendered per approach (so that the list display does not slow down in case of very large lists)