hard · Asset-Backed Securities waterfalls

An RMBS pays principal via a 'shifting-interest' structure: subordinate classes are locked out of prepayment principal early on, with their pro-rata share of unscheduled principal redirected to the seniors; the lockout steps down per a subordination-ratio schedule subject to delinquency and loss 'performance tests.' A senior support (AS/last-cash-flow) class absorbs the redirected subordinate prepayments. At year 6 the subordination percentage has more than doubled from closing (so the schedule would normally release subordinate prepayments), BUT the 60+ delinquency test is failing this period.

What is the most precise effect on the senior support (AS) class's WAL this period, and why?

  1. The AS class's WAL shortens because the failed delinquency test keeps the shifting-interest lockout in place, so subordinate prepayments continue to be redirected to the seniors, accelerating the AS class.
  2. The AS class's WAL lengthens because the doubled subordination forces an immediate step-down regardless of the delinquency test, releasing prepayments to subordinates and starving the AS class of cash.
  3. The AS class's WAL is unchanged because shifting interest only governs allocation of scheduled principal, while unscheduled prepayments are always allocated strictly pro-rata to all classes involved.
  4. The AS class's WAL lengthens because failing the delinquency test diverts that period's prepayments into a reserve fund instead of any bond class, effectively halving the AS class's scheduled principal receipt that period.

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