Systemsamplesize, my 2 cents worth, I am a place bettor from way back, still using the same method of selection though there have been a few tweaks over the years.

I've been using $100 bets for many years, though I have a lot of bets over the course of a week. A few years ago I decided that my method was good enough to increase stakes, I had $1000 bets in mind possibly spread over several bookies/ corp orates etc. but decided to cautiously increase in $100 increments.

I can't quite remember at what stage my usual 4% POT was shrinking, but certainly before I reached $500 bets; it had disappeared. I reverted back to $100 bets and presto it slowly hovered around the 4% POT again.

Now I bet most days, I noticed that there seemed to less effect on Saturdays and possibly Wednesdays, but on other days there was a definite effect on the Divvies.