First it might be good to know if its GBL or GHB you're dealing with. And then there's dilution of course so you can't compare your dosages with anyone else who doesn't have the same product you do!
Well you can but if you monitored the production process: Say you have made GHB from GBL then it's possible to make a saturated solution which has a concentration inherent to the substance. I.e. when it's any more concentrated it will precipitate out of solution. This is not the whole story, temperature has effect on it and if you don't know your chemistry this will become hard to grasp, the whole story that is.
You don't need to know anything about your product in fact, besides there's no poison in it and it's not something totally different than GHB or GBL. 1,4-BDO and stuff I have no experience with.
So what you do is you arrange for a method that lets you dose volumetrically, like say a syringe or a little plastic vial. There are those meant for GHB that are 4 ml. Next you carefully try a not to high dose, you're past this stage as you mentioned. Now next time just try a little more and see. Really, I don't think you won't notice the effects eventually. Just be careful because at some dose it will become near-impossible if not impossible to stay awake and you will technically be in coma (meaning you can not be aroused by any means) until you snap out of it like 3 hours later. It's risky because you can aspirate (suffocate) on your vomit if you don't wake up while vomiting.
For some people it's the art of dosing so much it feels absolutely amazing but not so much you will pass out.
A reminder: what your 'ideal dose' is doesnt necessarily go for the next guy, and like I said if you have another 'product', another source, another batch you need to start from scratch examining the way it works.
On a related note: I've come across some GHB that was not made that well so it still also contained GBL. This made it hard and weird to say what a good dosage was because not only is GBL more powerful by volume it has a stronger 'kick' to it which helped define the effect. Strange mixture....