Spectra pump setting

Mommies, I have been back to work for 2 weeks now and my lo is 14 weeks old. I have been using the Spectra S2. I used to have the pump on L04 vaccuum. Then my lo started sleeping longer at night and the amount of milk I pumped went down. So I increased it to L05 vaccuum and now get more milk. Is it normal to have to change settings even though you have used one setting for a while? With my firstbaby i used medela so it was very different.