starter not doubling but floating?

Hi!

I was wondering if anyone can help. I have a 100% hydration starter (6 weeks old). I retain a cup and feed it with 120g AP/plain white flour and 120g water, and after 2 hours, it will begin to float and increase in size by about 50% and I can continue to remove blobs that will float for around 2 hours, however, it never doubles in size, and from what I can see the starter should not float until around 6-8 hours after feeding [in general], would this starter still be viable?

Thanks in advance!

PS great resource thanks!