Oops, someone beat me to the answer. Glad you've got it figured out. Yeah, mixing two different solutions is NEVER going to give you higher than what the highest nic solution is. It will be somewhere between the two strengths.
Good question, though. It can come in handy if you can't find your exact strength (say you like 12mg/ml, same as saying 1.2%). You can buy a bottle of 0% and a bottle of 2.4% and mix the two to get your 1.2%. Easy peasy and handy info.
Now, if you want it stronger, buy yourself a bottle of 2.4%. Mixing equal parts of 2.4% and 1.2% will give you a 1.8% juice. HTH!