Why efficiency rises
If you provide between two prices rather than from zero to infinity, your capital backs the pool only within that band. Inside it, you behave as though you had deposited many times more, so you capture a proportionally larger share of the fees.
Narrower ranges produce larger multipliers, which is the whole attraction.
What happens at the edges
When the price leaves your range, your position converts entirely into whichever asset is now on the wrong side, and you stop earning fees altogether. You are holding a single token and waiting.
If the price never returns, you have effectively sold one asset for the other across your range — realised, not impermanent.
Range selection is the strategy
A tight range earns much more while it holds and exits quickly. A wide range earns less and survives more. Rebalancing to follow the price costs gas and realises the loss each time you do it.
This makes it an active position with a running cost, which is very different from how it is often described.
Who it suits
It suits correlated pairs where the price genuinely stays in a band, and participants willing to monitor and adjust. It suits volatile pairs and passive holders much less well, despite the headline yields being highest there.
FBT Swap surfaces liquidity and pool data from the underlying protocols with their source shown, and presents none of it as a promised return.