You always can sell all your shares, or part of them, to free...

You always can sell all your shares, or part of them, to free some funds and deploy them via the SPP ; I'm on the same camp as you, as I've topped up recently and my allocation to specky IMU is full, so I'm planning selling my 300k shares on the D-5 ( D= day of SPP closure), 2 days later on D-3 I'll receive the proceedings from this sale including a tax loss, and I'll deploy them on the SPP giving me potentially 2.5% more shares (2.5% discount), plus 300k options.

The scale back is a risk of not having all your shares back. But even if we have a 50% scale back, you get your original amount back ( 50% heads, 50% oppies) and you free 50% of your capital.

How likely is a scale back > 50% ? Who knows ...

Just my thoughts.

All the best !