Whatever you make fit it will be a max of 500ml..probably 400ml so not really worth having. If you extend the carrier further down you foul the charge port and still end up with the top of the smallest bottle rubbing the shock. ( I tried all of the that on my E180 RS using a Fly 550 bottle from Halfords which was the smallest I could find. I gave up on that in favour of a waist pack.
A waist pack combines the a bility to carry an aquapac plus tools/repair bits etc. Mine is a Camelbac.........it has the aquapac, first aid kit, energy bars, phone, and bike spares. Unlike a back pac you only notice you are wearing it when off the bike. On the bike the weight is low down on your waist which is ideally where you want it for loading front or rear wheel , and not moving about. The only slight downside is that it reduces in size as the amount of drink get used up so can require the belt to be adjusted after a while. That is easy to do on the Camelbac even when riding so not a big deal.
A £10 side entry cage, like this from eBay, works perfectly with a 550ml Elite Fly water bottle, it fits snuggly in my "small" E150 frame.
The Elite Fly bottles have a very shallow top.