iMac unlocks with Apple Watch right after putting iMac in Sleep mode

As my fingerprints don't stay recognised (Raynaud's Disease is the problem I think) I have allowed my Watch to unlock my iMac (running 26.2) However, when I select Sleep from the Apple menu, it immediately unlocks before I can walk away from the iMac. Is there a way to prevent this when I actually want the iMac to Sleep rather than shutdown? It does go to Sleep eventually but I don't necessarily want to leave it unlocked until it does.