First, make sure your build compares favorably to other LB/BMP builds in terms of sonic quality by checking out various clips, videos, and recordings. If you're sure it's working up to par, just not what exactly what you're looking for, then the tone stack is the place to start.
On the bottom edge of the board, you'll see a .0039 cap, two 39K resistors, and a .01 cap in the same general vicinity. These components plus the tone pot make up the tone network. You can adjust the component values to taste. You'll probably want to use the following tool. It has a Big Muff tone network built in, and you can dynamically view the results of value changes.
With that said, I haven't experienced a problem with flabby bass, or clarity for that matter, with triangle-based circuits. However, I'm usually playing through relatively low wattage American and Brit-flavored combos that don't have the bass response of a 4x12 cab to begin with.
With component value changes, you can certainly roll off some bass to reduce flab, but take a look at TSC and watch the curve as you increase the tone control setting. A rolloff of bass frequencies occurs accompanied by an increase in treble frequencies. So changing values just to get less/more bass or less/more treble doesn't buy you a lot over the control you already have with the pot.
While the tone control can dramatically affect bass and treble frequencies, watch the midrange on the graph. You don't have much control over that. The stock circuit has a sizable dip in the midrange around 1kHz or so. By changing a single component, you can increase this dip or flatten it. Most folks prefer to flatten out the dip as opposed to making it bigger, but I wouldn't necessarily call this an increase in clarity. It certainly helps to prevent your tone from getting lost in the mix by making it more forward sounding. An extreme example is the stock 808 circuit which has a pronounced midrange push.
Take a search for the mids scoop/flat/boost mod Keith posted a while back. That gives you the ability to have switchable control over midrange response. As of this writing, it's only about three posts down from this one.