Hi
Safety stock is also part of stock. If you have stock of 1000 and safety stock maintained is 500 then system will show 500 as surplus (as its demand element and while calculating in any planning run) but that doesn't mean that stock is going down. Safety stock is an extra demand element which will create more/maintain specific stock level only. If your stock drops below 500 it will try to generate more supplies (planned order/PR etc.) which should maintain stock level.
So, projected stock on hand is calculating this accordingly which means in your case you see 30. Of course you have safety stock of 5 but this does not mean you will not use when you have actual demand example SO. This stock level which you want to have so that you can meet unexpected demands or for other business reasons.
Think, if you now receive SO for 28. What should this mean in any business case? I have projected stock of 30 so I can meet this but now to maintain safety stock of 5 we need to produce 3 more.
But if I go with other approach this would mean I have 25 stock so I have to produce 3 to meet SO (considering priority is on actual demand elements).
Though if you want you can then add logic accordingly in the macro but think twice before you do so. Anyways its calculation to show certain situation.
Regards
Rahul