>>7741500
>>7741655
It looks like you're using a soft brush that is using opacity to gradually erase the dots. It's not that the dots are "getting smaller" those are the leftovers of the dots that have been scraped away. You need to use a brush that erases without opacity. You could even use the default g pen if you like, considering traditionally tone was scraped with razor blades. Pic related, just a patch of tone with straight lines erasing some dots close up. Avoid erasing on 45 degree angles.