I mean the cap runs at a lag average to the live market, so surely the live market at current levels isnt sustainable.
I suppose it doesnt/cant exist at £7k, demand destruction is deep, and quickly undermines the excessive price. Forward live price will be based on current projection of supply v demand for forward period. It wouldnt take into account a reasonably sudden 35% reduction say in demand whether domestic usage, industrial etc.
We saw a really quick snapshot of this with Covid. Fuels markets halved in price because you suddenly shut down 15% of fuel need with factories closing, leaving excess supply. But the flip side you've never had one guy controlling the destiny of a continents gas flow. Its 20% of norms coming through the key pipe to Germany. Will it be zero come winter or back up to 40%, we cant know and hence the heavy prices.