exactly... although what you said about [2A] + [2B] = 2 EXP it doesn't really... maybe when your alchemy is still low expect to have some jumps of few times EXP than one (I think) but really don't waste a lot of material you compound the best thing to do is [1A] + [1B] the EXP when higher level exp gets so slow...
take mine foe example... (or maybe many others) I had my alchemy superior at 13 (about 46%) It took me maybe (50-100 or more stack to have it level 14) (small wooden gear and took weeks since I can't really click many times a day...) so think about it :)

Hope it helps,
Dopeliiii