According to DoDI 5000.02, the decision to exceed the 10% LRIP guideline is the MDAs.  After the decision, the MDA must notify Congress via the selected acquisition report.  So, the report to Congress is not very detailed like a decision brief would be.  Normally, MDA rational includes matter-of-fact life incidences such as losing a test aircraft and being unable to finish a few critical points prior to the 10% mark.  Or, having supply issues that affect completion of required demonstrations or tests.  Bottomline, the rationale should make sense and the gist of the message should convey that except for this "issue" the MDA has confidence the system will be operationally effective and suitable.