Indeed, the stomach content could have played some role in rabbit's weak response to
GBL, however, Dexter supposes it would predominantly affect the come up time, not the intensity of inebriation itself.
There is other likely culprit too, i.e. the levels lactamase enzymes responsible for a conversion of GBL to
GHB in vivo. Those levels vary between individuals - if there is little of them, initial response to GBL will be weaker than expected. However, after a few ingestions their endogenous production increases and so the response to GBL does. Therefore beware of doing GBL in not favourable settings (i.e. in public) for a first few times - out of the blue your pet may be hit by a much more intense inebriation than expected, go down and wake up in emergency!
There is one more thing worth exploring in case of GHB inebriation, i.e. the role of the set & setting in a quality of it. Alf found out it really changes the experience considerably: there is a huge difference between doing G alone at home and doing it in a nice company.
Runitsthepolice is absolutely right, initial dose of 2.5ml of GBL (= about 4g of GHB) on an empty stomach is really a lot, actually enough to put a creature to sleep for a few hours. So, instead of increasing doses let a body learn how to metabolise GBL and then try again with initial dose of 1-1.5ml of GBL = 2.4g of GHB should really do the trick. Don't forget that rabbit's psyche too should learn recognising symptoms of GHB inebriation as they can be quite subtle and considerably dependent on set & setting. All this can take a few disappointing tries, so at least make those tries as safe as possible, G is not a joke.