@rhc you’re mixing up different concepts here.
Box 2 has nothing to do with sales, it is only for cases where you’re buying from a vat-registered supplier elsewhere in the EU and you have told them you’re registered for vat in the UK - they don’t charge their vat to you but you have to put the appropriate UK vat in box 2 (and the net in box 9).
When selling goods to a customer elsewhere in the EU who is registered for VAT in their own country you would normally not charge them any UK vat, and you would include the net value of the sale in box 8 - this much is uncontroversial. The OP’s question is whether you have to include in box 8 the net value of sales to non-vat-registered customers in the EU where you are also charging them UK vat as you would for a UK sale.
The quoted HMRC guidance is ambiguous - on the one hand it seems to suggest you should include these in box 8: “all supplies of goods to other EU member states … Leave out any VAT.” but then it goes on to qualify this with “distance sales to unregistered customers in another member state where the value of your distance sales have exceeded the distance selling threshold of that member state” which suggests you only include such sales if they’re over a threshold.
However if you follow the link to VAT notice 725 it becomes clearer. Section 6.17 has a table that lays out what goes in which box - it says that distance sales from the UK to the EU below the threshold at which you would have to register for vat in the destination country do not go in box 8, only in box 6.