My experience with blend controls has been less than thrilling as well, so I don't do it anymore. I guess I just don't appreciate the fine subtleties available from that scheme as much as some do.
Those microcoil pickups are surprisingly proximity sensitive, so adjust slowly or you may miss the sweet spot.
Volume (and to a lesser extent, tone) controls that have most of their action in a narrow band at the extreme throws of the pot usually result from using "linear taper" pots as opposed to "audio taper". The human ear has a logarithmic response curve, so linear changes in loudness/frequency aren't perceived as such.
If you did use log (audio) taper pots, it's possible they're of too high a value. The way impedances work out between guitar pickups, cables and amplifiers, 500K pots work best more often than not. 250K pots tend to eat a little high end off the signal, while 1M pots tend to have lop-sided response characteristics such as you're experiencing. If you used 1M log taper pots, you may be able to get a satisfactory response out of them without replacement by simply tacking a 1M resistor across the outside terminals of the pot. It's not a perfect solution, but it's close enough for government work. Modern pot tapers don't follow a log curve as closely as is implied anyway.