Purely from reading that I can tell you aren;t very well versed in the subject. There are different strains of psilocybin mushrooms. Diferent strains that look different. You can have very small caps and stems or large, or ones like the size of mushrooms on a pizza. SO 3-4 booms does not equal an 8th. Far from it in my experience. even HUGE caps and stems won't weigh that much they would have to be large for them to weigh that much dry. real large.
Also psychedelics vary person to person to tell him he is going to focus too much is misinformation. he may focus on one thing or idea for 6 hours hey may not be able to keep his mind on one thing for more than 2 seconds.
You can;t kinda trip, like then is it even considered a trip? if you took a half eighth you can trip. if you ate one cap and one stem if you felt anything at all it would probably be just a funky essence of body high
also quality counts for something. I have eaten a quad and i didnt trip as hard as i did on this 2.5 g's that i took at another time.