Liquidate maximum percentage is weighted

In the below liquidation code, there is a limit to the percent of an underwater user's debts liquidated in a single call to liquidate. The hardcoded constant percent is 20%.

public(friend) fun liquidate<P>(
    // [..]
    // we can liquidate up to 20% of the obligation's market value
    let max_repay_value = min(
        mul(
            obligation.weighted_borrowed_value_usd,
            decimal::from_percent(CLOSE_FACTOR_PCT)
        ),
        borrow.market_value
    );

However, as can be seen from the code above, the actual amount liquidatable in a single call is actually based on the weighted value of the debt. This is merely unusual and not a defect of the protocol.