What the tiers are for
Pairs that barely move against each other — two dollar stablecoins, two wrapped forms of the same asset — use a very low tier, often a few hundredths of a percent, because providers take almost no inventory risk and the business is volume.
Volatile majors sit in the middle. Exotic and newly launched pairs charge the most, because a provider there is genuinely likely to end up holding the wrong side.
Why the cheapest tier does not always win
The same pair often exists in several tiers simultaneously. A router comparing them does not pick the lowest percentage; it picks the best net output, and a higher-fee pool with far deeper reserves frequently beats a cheap but shallow one.
That is the correct answer even though it looks wrong on a fee comparison, because price impact on the shallow pool costs more than the fee difference saves.
Concentrated liquidity changes the shape
Newer AMM designs let providers place liquidity in a price range instead of across the whole curve. Inside that range the pool behaves as if it were enormously deeper; outside it, the liquidity is simply not there.
For a trader this means depth can vary sharply with price. A pair that executed beautifully yesterday can be thin today because the price has moved out of where the liquidity is concentrated.
Separating it from the platform fee
The pool fee goes to liquidity providers. The platform fee is what the interface charges — on FBT Swap, 0.70% of the input on supported routes, shown in the quote before you sign. Gas goes to the network.
Three recipients, three mechanisms. Any comparison of swap venues that only counts one of them is incomplete.