Yield Scalability and Market Impact

In Decentralized Finance, yield is rarely a static figure. For an Atomist curating a Fusion Vault, selecting the market with the highest "headline" APR is only the first step. To truly optimize a vault's performance, one must account for Market Impact—the effect that the vault’s own capital has on the equilibrium of the target protocol.

This page explains why Fusion vaults often distribute capital across multiple markets, even when one appears to offer superior returns, and how to approach allocation limits through the lens of yield scalability.

The Scalability of Yield

Most DeFi yield strategies (particularly lending via Aave, Compound, or Morpho) are not infinitely scalable. The APR offered by these protocols is a function of the Utilization Rate ($U$).

The Utilization Rate is defined as:

$$U = \frac{\text{Total Borrows}}{\text{Total Liquidity}}$$

As a Fusion vault supplies more assets to a market, the Total Liquidity increases. If the Total Borrows remain constant, the Utilization Rate decreases, which in turn moves the market down the interest rate curve, reducing the APR for all suppliers in that pool. This phenomenon is known as Yield Slippage.

Interest Rate Curves and "The Kink"

Most lending protocols utilize a "kinked" interest rate curve. This model ensures there is always liquidity available for withdrawers while incentivizing borrowing up to an optimal point ($U_{opt}$).

The interest rate $R_t$ typically follows a two-part slope:

1. Before the Kink ($U < U_{opt}$): A shallow slope where interest increases slowly to encourage borrowing.

2. After the Kink ($U > U_{opt}$): A steep slope where interest rises sharply to discourage further borrowing and attract new suppliers.

The Impact of Large Allocations

When a market is operating "above the kink," it offers an elevated APR because liquidity is scarce. However, these markets are also the most sensitive to new capital.

If an Alpha sees a market offering a headline APR of 12%, it might only take a relatively small deposit to push the utilization back below the kink, causing the APR to drop precipitously to a base rate (e.g., 4%).

Marginal Yield vs. Average Yield

The goal of a Fusion vault is often to maximize the aggregate yield of the Total Assets ($A_{total}$) across all integrated markets. The Alpha must calculate the Marginal Yield—the yield generated by the next dollar allocated—rather than relying solely on the current headline yield.

The Mathematical Rationale for Splitting

To illustrate the impact of yield slippage, let's assume the following interest rate model:

• Optimal Utilization ($U_{opt}$): 90%

• Slope 1 (Below Kink): 4% max

• Slope 2 (Above Kink): 60% max

An Alpha has $2,000,000 USDC to allocate between two markets:

• Market A (thin liquidity):

  • Total Liquidity: $10,000,000

  • Total Borrows: $9,500,000

  • Current Utilization: 95% (Operating high on the steep slope).

  • Current Headline Supply APR: 29.07%

• Market B (deep liquidity):

  • Current Headline Supply APR: 6.00% (Stable; deep enough that a $2M deposit has negligible impact).

Scenario 1: Single Allocation (The Yield Trap) The Alpha chases the 29.07% headline rate and allocates the full $2,000,000 to Market A.

• New Liquidity in Market A: $12,000,000

• New Utilization: $9,500,000 / $12,000,000 = 79.16%

• Because utilization has fallen below the 90% kink, the market crashes down to the shallow slope (Slope 1).

• New Supply APR on Market A drops to 2.51%.

• Total Annual Yield: $2,000,000 $\times 2.51\%$ = $\mathbf{\$50,200}$

Scenario 2: Distributed Allocation (Optimal Splitting) The Alpha calculates the capacity of Market A and decides to split the capital, allocating $400,000 to Market A and $1,600,000 to Market B.

• Market A ($400,000): New Liquidity is $10.4M. Utilization drops slightly to 91.35%. Because it stays above the kink, the new Supply APR remains strong at 9.93%.

  • Yield from A: $400,000 \times 9.93\% = \$39,720$

• Market B ($1,600,000): Earns the stable 6.00%.

  • Yield from B: $1,600,000 \times 6.00\% = \$96,000$

• Total Annual Yield: $\$39,720 + \$96,000 = \mathbf{\$135,720}$

By strategically splitting the allocation to respect the target market's "kink," the distributed strategy generates over 2.7x more yield ($135,720 vs. $50,200) than simply dumping capital into the market with the highest headline APR.

Examples

Good examples of split asset allocation for yield optimization are the stablecoin lending optimizers of the IPOR Fusion DAO, like the IPOR USDC Prime: