A Binary Search for the count of items that are less than a specified value

FindLessThan.cs

using System;

public class FindLessThanInOrderedList
{
    public int ArrayCalls { get; private set; }
    
    public  int FindLessThanBinarySearch(int[] numbers, int lessThan, int startIndex = 0, int endIndex = -1)
    {
        if (endIndex == -1) endIndex = numbers.Length - 1;
        if (endIndex - startIndex < 2)
        {
            return SmallArrayCheck(numbers, lessThan, startIndex, endIndex);
        }
        int midPointIndex = (endIndex - startIndex) / 2 + startIndex;
        var midPoint = numbers[midPointIndex];
        ArrayCalls++;

        if (midPoint >= lessThan)
            return FindLessThanBinarySearch(numbers, lessThan, startIndex, midPointIndex - 1);
        return FindLessThanBinarySearch(numbers, lessThan, midPointIndex, endIndex);
    }

    private int SmallArrayCheck(int[] numbers, int lessThan, int startIndex, int endIndex)
    {
        ArrayCalls++;
        var endValue = numbers[endIndex];
        if (endValue < lessThan)
        {
            return endIndex + 1;
        }

        ArrayCalls++;
        var startValue = numbers[startIndex];
        if (startValue < lessThan)
        {
            return startIndex + 1;
        }

        return startIndex;
    }
}

Array calls should max out around 15 accesses, even on the largest arrays