@dc42 All correct insights. In my case I'm running a Voron 2.4 build so no bed plate weight, just a lighter gantry, and the gearing down of the Z motors means I'm a bit less worried about the full micro step issue as it is by ratio a smaller final Z distance The "four full steps" however is worth further consideration.
I think my PSU holds enough residual current to give it a decent boost as it's about twice as powerful as I need, hence why it manages to raise Z noticeably (looking at the cubes I test I reckon about 2.6mm). I completely agree that the power likely cuts out a bit too early to complete the full raise so I have been following another thread and ordered up some 10,000 uF capacitors to stick across the power input to try and store a bit more juice.
The root issue of not homing is still valid though. There are many people who don't have the space or ability to mount an upper Z EndStop but more importantly the documentation mentions continuing without homing as a theoretical (but not recommended) possibility. So having a way to cover that base for those who need it seems wise.
Your suggested code has worked perfectly for that so thank you!