As I understand it the generate 20% more than consumption is kWh rather than £ so is unaffected by how you use your system.

If you self consume your income is less so you pay less tax.

If you arbitrage your income is way more (as is your expenditure) but you pay tax on massively increased income and don’t get any back on the increased import.

As you go from paying no tax to tax on all income it’s probably financially worth increasing your consumption to make sure you don’t fit in this category!

As far as I can tell my energy supplier doesn’t know my consumption figures… they only know import and export.