Stentor wrote:"Bitter" would suggest the temperature being too hot or possibly - but less likely - too much time. You are extracting something you do not want to extract. That usually happens when you cross a certain temperature threshold below which the undesired (bitter) substances do not get extracted.
Too much leaf gives quite a different sensation. Maybe give it a try with a cheaper tea and really overdo the leaf to water ratio so you can be sure you're not confusing "too strong" with bitterness. This should narrow it down to what parameters you need to be tweaking.
Hope this helps!
I just want to report I got a successful brew this morning. Lowered the temp just a smidge and adjusted the leaf to water ratio a bit and brewed as per O-cha's instructions. I have flavor and umami.