thats the hose/regulator ID causing the lack of power WCA.
the aldi regulator has a 6mm flow path ID. which is a bit of a joke.
i have just tapped direct into the 1/2 inch thread on the end of the reciever with my own large ID regulator and had much better results – of course that means the length of time you can use your tools is much reduced.
i have a 100 litre and a 24 litre set up in tandem like this – i have them in a different shed to the garage as the noise would be unbearable.
I run air guns/spot blaster/DA sander, air grinders and have sprayed my whole land rover with that set up.
Rusty macs unit is nice and compact and fairly useful in respect to running air tools – would be ideal starter unit for any workshop with an air requirement. – although overkill for just inflating tubeless tires 😉