spp what are we allocated?

Hi I am just a small holder with only 3000 shares (in the red by a lot), dont want to pre-empt the SPP document but what usually happens in these situations do we get to buy shares relevant to how many we hold or as someone else mentioned do we all receive the same allocation say 5000 shareholders X $3000(worth of shares each )= $15m

It seems unfair especially for the larger holders, also if someone was to purchase only a few shares before the record date are they also entitled to the SPP?
Why do companies do these SPP this way is it more economical ?
Any answers appreciated.