The slivers of goo in bulbs with containment 4 are really hard to target, harder still to see, and just generally unpleasant and not visually "good".

Experiment with other techniques for displaying how much is in the tank.

The first port of call is to display a logarithmic representation of the quantity in the bulb, making it so that small and middling quantities still take up a respectable amount of the space in the tank, while still showing a relatively clear indication of "progress" that slows down the more full it gets. The representation would then be divided proportionally among the goo in the bulb, but would still be required to respect the "minimum" rules in order to avoid making small goo amounts virtually untargetable.

Alternatives to this include showing the bulb as full when sneaking (or perhaps even always), suggested by Ento, and possibly other techniques I haven't thought of yet.

Serious rework of the display procedure and how the bulbs render and calculate fluid heights, and I feel like this is the final result.