An attempt was made to explain, along with the definition of CovSig, here: bolts/XX-eltoo-transactions.md at a17b60f42077a785c625430e8f6e8e2828d4d898 · instagibbs/bolts · GitHub
proposed method to remove round-trips without CTV-like application, or the annex usage: Avoid round-trip with scriptless scripts · Issue #5 · instagibbs/bolts · GitHub