30 mins is cutting it VERY CLOSE.
If a runway is closed due to a crash, one can usually divert somewhere within 30 mins flying time.
If (much more likely) one gets caught by unforecast weather, 30 mins isn't likely to be much good. Unless it's just a bit of local fog.
But, common PPL (training scene) practices make such reserves a complete farce. The best one I was taught is relying on the paperwork for the endurance. I used to have "disagreements" with the CFI over insisting that I fill right up. In the end, both schools I trained in (UK PPL) ended up with multiple planes going down; one of them into a house. Has anything changed in procedures? No.
There are also many places in Europe where limited avgas availability means anything less than 3hrs is no good
