| My unofficial answer is "Sort of". I'm a recovering notorious string mixer and in theory, a well conceived matched set should be balanced. The gauge shouldn't have any crazy jumps and it tracks that if your bass is set up properly, the intonation points should line up predictably too.
I've played with brighter low register strings and darker high register strings, metal low with synth or gut high, etc. I've come up with some good combos, but there's always some evidence that you're not playing a matched set. Intonation might be one indication. Feel. Sound fundamental. Volume. Bow response (if you use one), etc. It's never a matched set.
That being said, the string companies don't always do a great job of balancing their sets. Pirastro has a few sets where the E seems one gauge off and a common fix is to go up a gauge in the same string set for the E. I know people who do the same thing with Spirocores. Most people agree that the Evah Pirazzi regular set has a slightly mismatched G string, sonically. So, having perfectly balanced set just by getting them all out of the same pack is not a sure thing. But, some sets are well balanced. I don't know anyone (who I believe) who claims to have a perfectly balanced mixed set.
Then there's the question of setup. I don't know how much experience you have with your bass or swapping strings, but a lot of difference can be made in sound, feel, tension, tone, etc through setup. I'm suspicious if you're trying to beef up one of the middle strings (A) that you've either got a bad set of strings now (or a bad string) or you've got a setup problem. It's a longer discussion and one you should have with a luthier, but I would think about having it before you go down the holy grail quest of the perfect mix and match string potion. It's the road to heartache and ruin...trust me.
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