Im not really sure the thinking behind the additional first year tax imposed for vehicles over £40k, why that particular figure. I can understand you'r annoyance at the added tax.
For me, Skoda would not budge from the additional £888 they wanted from us, despite with the help you all provided on this forum pointing out the difference was actually £660 as they had not accounted for the tax that was already included pre-april, so we refused to accept a revised contract out of principle and we now have a Mercedes GLB 200d AMG premium arriving next week