I'm having a bit of trouble brewing this gyo properly. Do you mind sharing your brewing parameters?
I do a first infusion at 150 degrees--30-60 seconds--to get a sense of whether it seems just right or not enough, and use that as my guide to later infusions. The next infusion is always shorter, and I usually try at least one more at that temp before upping the temp to 160, 175, 190, and eventually I get a few infusions at 205--some up to a couple of minutes--before I stop.
As for how much tea/water, well, I use about twice the amount of sencha I'd use for the same size vessel. Since I've only done this tea twice (newly opened bag, first time buying it), and I didn't measure either time, all I can say is that the brewing vessel was about 1/2 full when leaves were thoroughly rehydrated. Today's office infusion was different because I deliberately overfilled in order to have enough (via increased # of small infusions) to share.