Before or after taxes, the discount isn't 50% from BOS.
But it almost certainly is before YQ. When a full third of the fare is not discounted it is hard for the percentages advertised to make a ton of sense. There are a few T fares (only L & T qualify) published from BOS-BUE:
Export from Wandering Aramean Travel Tools
Code:
Flexible Fare Search -- BOS-BUE roundtrp for date range Jun-Dec on carrier UA -- United Airlines
Carrier|From |To |FareBasis |Fare |Min |Max |Adv. Purch|Earliest |Latest |
UA |BOS |BUE |TLXAR3 |USD$ 797 |3days |90days |seerules | | |
UA |BOS |BUE |TLWAR3 |USD$ 848 |3days |90days |seerules | | |
UA |BOS |BUE |THXAR3 |USD$ 918 |3days |90days |seerules | | |
UA |BOS |BUE |THWAR3 |USD$ 969 |3days |90days |seerules | | |
UA |BOS |BUE |TPXAR3 |USD$ 1020 |3days |90days |seerules | | |
UA |BOS |BUE |TPWAR3 |USD$ 1070 |3days |90days |seerules | | |
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But those prices do not reflect the $320 YQ that UA is throwing in on top of the fare. This exact scenario is one of the reasons airlines very much prefer to roll out the YQ rather than a single, inclusive price. Surcharges are not discounted.