Here is the link which gives the full details - great stuff if you like your nested formula's
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/707897/2017-18-exc-indi-v1.pdf
Have just run it through BTC and my tax figure is the same as yours with no exclusion warnings being thrown up.
I have just tested BTC for 2 know exclusion cases including number 70
and rather worryingly the calcs are not flagging up the exclusions they should flag up - they are using the incorrect higher total of tax- oh b*******s.
this being the case it does look like there is a more favorable calculation available that will involve the paper route or filing online and asking hmrc to amend (if that is possible?)