A curve pots aren't actually logarithmic. They are usually 2 or 3 linear sections that roughly copy a log to base 10 curve (remember high school maths?). If you bust open an A pot, sometimes you can actually the see where the different linear sections start and finish in the carbon track. And as you've found they can really jump around in audio response. Personally I use A pots for vol, but I have no problem wiring my customer's vols with linear if they request. I've even suggested it for some guys too, after hearing about their playing style and the gigs they do etc etc. A vol pot in a guitar has a very different role than that in a hi-fi or studio application. Often in a strat or something, it's more a distortion control, than a loudness control. And for us bassists, it's pretty rare we run our vol below 80% of full loudness in the real world of gigs and sessions. If you need to finely tweak this region then a linear pot is ideal as half of its rotation takes you from 90 to 100% loudness.
Just as each stick of timber that's glued together in your guitar works together to affect its response and acoustic tone, volume pots are just one part of an electronic network and, especially in passive basses, do not work in anything even resembling isolation. The effect they have on tone in passive basses is well known, but they way they work when blending two pickups is widely misunderstood.
Congrats on the solder job! I'd use a few cable ties to neaten up the job. They don't actually do much unless you have to anchor battery clips or something, bit it makes things look a bit more pro.