Someone once explained to me that electricity and hydraulics are very similar. When flowing they always try to take the easiest path.
Your schematic is upside down from a real engine. The oil has to flow upwards to get to the main galley. You are assuming it will make a sharp right had Turn upwards when it could make a left turn downwards without the plug. It could flow a combination multiple directions all at one hence the terms low or erratic pressure. It could go through the filter backwards even.
I know those passages too. I drilled all mine larger on my new build.
You can disagree with me if you want but you know that plug needs to be in there. I've offered you a possible explanation and you don,t agree. That's ok.
