Its the same with most drugs the mind is..
You wont notice as much of a high as u might of the first time just like with most drugs its all about the first come on of the drug or the first few hours. Thats probably why IV opiate users overdose cause they want that first hit to be the best. If they could get as high by doing multiply dose's spread apart i think there would be a lot less deaths. With codeine CWE I drink 1000mg over a few hours to try to beat that ceiling dose of ~400mg. I also use other substances but thats another story.
Yeah like i said with most drugs you notice them more when they come on fast as the mind doesn't get a chance to get used to the change.
Try some other drugs to mix in take it slow. Like maybe try some of these drugs with it (not all at once) phenergan, soma, quinine, dramamine, benzos, Catapres (Clonidine), check out opiate potentiators i think the best info on it to date is on an opiate website i can't recall called opiod.org or something along those lines.