What size hot water storage tank with heat pump?

Roughly about 40cm between head and [Duschkopf]

We got by well with 5 people and about 140 liters of hot water storage. However, that was with a gas heating system (50-55°) and it was really rare that everyone showered one after another within a short time frame. Now, as two people, and since it is not necessarily required to shower daily, the hot water storage is naturally much too large.

Does anyone know this effect too? Same fitting, once fixed shower head once handheld shower and despite thermostat battery different temperatures?

Yes, I know it. With the rain shower there is a feeling of cooler air in between – that's how I explain it.

Regarding the question: if the calculations are already tight, and we talk about scenarios warming up in the shower without a bathtub, maybe also the small wash while the last one showers, I wouldn't build a house for that – I mean, for calculating, because it might get tight and I would have to practice restraint because the family has their needs. -> 300 liters!
Showering behavior is also individual: I am done after 2.5 minutes, while the shower only runs 1.5. My husband showers for 15 minutes and doesn't want to have to stop because it gets cold. Sometimes you like it economical, sometimes you need pressure… -> 300L!

P.S. such a beautiful Raindance 300mm showerhead has, for example, up to 17 liters flow at 3 bar water pressure. A lot of hot water flows through there