Jo --
I don't want to be a pain in the posterior but you really, really, really, need to start testing at night. You need to get at least one spot check during the PM cycle. We encourage a before bed test on a daily basis. Of course, this depends on when in Scratchie's cycle you go to bed. Many of us like to get a +2 test. It can often signal if you need to get more tests in (i.e., if your +2 is much lower than your pre-shot test, it is likely to be an active cycle).
I do not feel comfortable making any recommendation about a dose increase without knowing what's going on with Scratchie's numbers at night. Many cats experience lower numbers at night. As it is, you're missing half of your data.