Drug tollerance vs Saturation point

Factual Questions
1

I am wondering if this particular issue has ever been addressed from this angle. I always hear about building up tollerances to certain drugs. I have zero familiarity with any drug besides pot so I will use it as an example.

One individual can smoke a small amount in the morning and stay high for 8 hours. Another individual can smoke the same pot at regular intervals throughout the day and not feel strong effects beyond a little rush directly after smoking. 

At first glance this looks like a case of someone who has developed a tollerance for the drug. But, if the first individual changed his habit one or two days and smoked at regular intervals he would also experience a reduced intensity. To me this sounds more like an example of saturation instead of tollerance. Has the concept of saturation been studied much?
2

You answered your own question. What you’re asking about is indeed saturation. Person A and Person B are smoking the same amounts, but all at once versus spread over multiple doses.

Tolerance would be more like: Person A smokes set amount at 8 am and stays high for 8 hours. Person B must smoke (set amount+x) in order to acheive the same high.

Unfortunately, I can’t point you to any studies. But maybe using the correct term will help you with your Google-fu?