request plus query latency is high due to slow indexer scan times

Query latency with request_plus is much higher than with not_bounded. While this is expected the request_plus query times are far greater than we expect. Below are links to two reports from a recent build (3151).

not_bounded (80th percentile, 272ms): http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=hades_400-3151-enterprise_8c9_access
request_plus (80th percentile, 5 sec): http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=hades_400-3151-enterprise_fba_access

All of the currently recommended indexer settings were used for this test.

[12/Jun/2015 17:28:13] INFO - Changing 2i setting indexer.settings.persisted_snapshot.interval to 20000
[12/Jun/2015 17:28:13] INFO - Changing 2i setting indexer.settings.compaction.check_period to 1200000
[12/Jun/2015 17:28:13] INFO - Changing 2i setting indexer.settings.inmemory_snapshot.interval to 200
[12/Jun/2015 17:28:13] INFO - Changing 2i setting indexer.settings.max_cpu_percent to 2400
[12/Jun/2015 17:28:13] INFO - Changing 2i setting indexer.settings.log_level to error
[12/Jun/2015 17:28:13] INFO - Changing 2i setting indexer.settings.scan_timeout to 0
[12/Jun/2015 17:28:13] INFO - Changing 2i setting projector.settings.log_level to error