Let's take a look at this way of thinking. In your example, you...

Let's take a look at this way of thinking.

In your example, you are planning to increase your holding by about 10%, so you choose to pay more money to take part in the SPP in order to avoid harming the bulk of your holding.

We can talk a step back and just think for a moment, just conceptually, and consider that if I do or don't take part, it impacts the value of your holding exactly the same amount as if you do or don't take part. Many many people will or won't take part, they'll buy on market or through the SPP or not at all. You are just one person. Whether or not you take part directly impacts how much money you are spending, but no more impact on the value of your shares than any of those many many others.

This should already illustrate how insane it is to justify taking part in the SPP from a personal value/investment perspective (if you want to donate money because you're happy to have less money in order to be generous, hey, you do you!), but if you're still not convinced, we can crunch some numbers...

In your example, we're adding 10%. Okay, so let's say we have 100,000 shares at a current value of around $52,000 and we're going to add 10,000 shares. We can either spend $5,500 with the SPP or we can buy on market at today's closing price of $5,200. The difference is $300. This equates to 0.3c (the best part of a pip) per share on the 100,000 shares you initially held. Do you think that every person who takes part in the SPP is adding the best part of a pip to the share price???

If these figures seem nebulous, let's look at it another way. The current market cap of SYR is about $425,000,000. One pip at the moment is over four million dollars. So, for it to be in your own best interests to buy through the SPP rather than on market, your purchase of $5,200 worth of shares through the SPP would need to add 60% of one pip in value to the company, which is over two million dollars! I trust I don't need to explain that purchasing $5,200 worth of shares on market rather than through the SPP does not harm the company to the value of over two million dollars.

If you take part in the SPP, you are throwing money away. The tiny, tiny benefit to the company is absolutely negligible. If the extra money you are spending fills a bucket, you are not even giving a drop to the company.

If anyone thinks that from a personal perspective it makes any sense to take part in the SPP, they are radically incorrect and have no grasp of numeracy. If anyone tells you it's in your best interest they either have no grasp of numeracy or they are lying to you. Either way, it is a clear indication that you should never take advice from such a person.