Yeah, I remember back in the days when meph you got was almost pure, those were the good days.
To be honest I would bomb 400mg minimum of good, barely cut meph so that is most likely your reason so your dosage was most likely too low and due to the state of meph nowadays it was most likely cut. Try railing it next time, I wouldn't bomb meph unless I had a large source of it.
I recommend taking a decent sized line, then keeping it alive with smaller lines. I find that once you reach your peak on meph you wont get any higher unless you take a lot more than you previously did, so it's best to get as high as you can and then keep it going.