"Anyone able to do some back of the envelope calculations as to...

"Anyone able to do some back of the envelope calculations as to what any possible scale-back could be with say 50%, 75%, 90% of holders taking up the $30k spp? I can't seem to find any shareholder count / capital structure info."

Share holder data is usually provided at the end of annual reports. See table below
.
Allowing that share holders with 5000 or less shares may not have spare cash lying around to throw at an SPP, as of 23 Sep 2020, there were 6647 share holders with more than 5000 shares.
If only the holders with 5000+ shares apply for the SPP, and none of the smaller holdings apply, then their average allocation out of $50m would be $7,522.

However, as per the note on slide 27, the company has reserved the right to accept more or less money from the SPP.

"This is not a limit on the amount to be raised under the SPP and Evolution may decide to accept applications (in whole or in part) that result in the SPP raising more or less than this amount, in its absolute discretion.
Should any scale back benecessary, scale back arrangements will be made on a pro rata basis to existing shareholdings (subject to any minimum dollar allocation determined by Evolution at its absolute discretion)"

My suspicion is that they will probably increase the allocation if they are offered more than $50m.
As always, you pays your money and takes your chances as to what you get allocated.

Cheers

Distribution of Fully Paid Shares (as at 23 September 2020)
RangeSecurities%No. of Holders		%
100,001 and Over1,571,853,42992.00	214	0.87
10,001 to 100,00084,050,3604.92	3,265	13.29
5,001 to 10,00023,680,2221.39	3,168	12.89
1,001 to 5,00024,990,3371.46	9,461	38.51
1 to 1,0004,038,8920.24	8,461	34.44
Total1,708,613,240100.00	24,569	100.00
Unmarketable Parcels16,6570.00	852	3.47