Yes, resin level will fall when water is added - but you can put more in if you want before the final 'topping up' with water.
The point was - NOT to try pushing the resin tube/filter down through DRY resin (which was how I originally tried to do it!)
Mike
To be fair I missed that point mike (sorry was not getting at you),
I was told years ago to fill 3/4 I said the same thing also about having 2 di's , 3/4 will go down, fill to neck as I said it will settle at the right amount add another di and it will last longer I said this to the supplier. The suppliers will do not offer this as standard as it ups the price I said this to the the supplier because I did the homework and still today nothing has changed it because some want to go for the cheapest price that will cost the alot more over a year :

they talked me round me on that point and I got another di vessel couple of months later off my own back..