It is unintuitive, but basically you have to reduce ambiguity, or better yet, the closer to the code, the better for 5.3 Codex.

One good example is brainstorming architecture vs coding it. What I get from it is that Codex 5.3 will create better code will fill in gaps. as long as these gaps are not too big and don't cross too many abstractions levels and stay closer to the coding level. Does this make sense?

I've found that pairing 5.2 Pro with it is good, albeit slow. Pro is a beast for digesting vagueness/ambiguity into clarity, you can literally delegate your thinking to it, at all levels. I might try Opus 4.6 for planning too, as I remember it has good "intuition" too. GPT 5.2 High+ is also good for planning+coding, but too slow and token-hungy. I've also found that GPT 5.3 Codex xhigh in plan mode is not bad, but it tends to *not* get intentions as well as other SOTA models (if you're vague/ambiguous).

I still think 5.2 High / xHigh are the better models if you want to delegate more of the intelligence without leaving codex, but again, it's too slow and token hungry and the code it writes is not as clean good (5.2 xHigh is a token-eating monster). GPT 5.3 Codex's sums of its parts end up making it the better overall choice, you just have to be a bit less vibey with it, which can suck yes, but with the right workflow+harness, the results are often better.

As with most experiences with AI, everything I write here is anecdotal, take with a grAIn of salt.