If I was doing 7oz I would put in about … 2.5 oz of how water, add powder, mix, then add the rest of cooled boiled water. Approx that anyway. It depends a bit how hot your hot water is - ie. Is it 100 degrees straight from the kettle or a bit cooler from a flask that you have been carrying for a few hours.
The bigger the bottle the easier it is, it’s small bottles I find - of 2 or 3 oz where it’s a bit harder to have enough hot water to mix the powder, but not too much.
If I was doing 7oz I would put in about … 2.5 oz of how water, add powder, mix, then add the rest of cooled boiled water. Approx that anyway. It depends a bit how hot your hot water is - ie. Is it 100 degrees straight from the kettle or a bit cooler from a flask that you have been carrying for a few hours.