The comment about using a heavily oxidised (?) tea like lapsang souchong or Russian caravan made a lot of sense.
This comment awakened my inner pedant:
Traditionally the tea leaves are placed in a sealable glass container, covered right to the top with cold water and placed in the
fridge for 4-120 hours. I usually use a 5l jug with glass clip lid or bamboo screwon top.
I can't think of too many traditions that involve a fridge
People in glass houses... My own word choices are just awful sometimes.
Anyway, the chilled water concentrate method sounds like it could handle a greater range of teas without making bitterness.