I created a test that uses X-DFDL-US-ASCII-7-BIT-PACKED encoding with a sequence with two elements with explicit length of 2, so I would expect it to need 28 bits total but it seems to want 30. Here's the error:

[error] Test edu.illinois.ncsa.daffodil.section11.content_framing_properties.TestContentFramingPropertiesDebug.test_packed7BitASCII10 failed: edu.illinois.ncsa.daffodil.tdml.TDMLException: Parse Error: Insufficient bits available. Required 14 bits, but only 12 were available.

[error] Schema context: element.s2 Location line 268 column 12 in file:/tmp/packed7BitASCII5940072276120378281.dfdl.xsd

See test_packed7BitASCII10 in:
daffodil-test/src/test/scala-debug/edu/illinois/ncsa/daffodil/section11/content_framing_properties/TestContentFramingPropertiesDebug.scala
daffodil-test/src/test/resources/edu/illinois/ncsa/daffodil/section11/content_framing_properties/ContentFramingProps.tdml