Now the way to test this is fairly simple, if you are familiar with the aunkai pushout
exercise, you know that if someone is leaning, you can pull away and they fall forwards because they have committed their weight forwards instead of keeping it down. A similar thing may happen with the arms, if your arms are tense and your partner pulls away, your arms will stay up. If your partner pulls away and your arms drop, just like a weighted chain would when you unhook it from a pole, then your arms are relaxed.
there is a 'third way' with the arms, the phrase you use, that I have bolded, I refer to as 'collapsed', not relaxed. You can keep 'collapsed' arms in the air with the mind - no tension, no push, just extended ki/mind (of course there must be some muscular input somewhere, but only enough to keep the hand at a fixed point in space), this for me is relaxed. The connection must be direct from the dantien to the hand. In my limited experience, the shoulder muscles are the biggest obstacle to finding the right feeling. The hands should be 'slaves' of the movement of the centre.