Thanks for the replies and hints. I still have a problem however with
nested queries/SP calls. Crystal Reports essentially runs a query

select * from ProPXSelectProfileResults(x,y,z)

where the source is a SP that in turn executes a query. The plan
is reported as
PLAN SORT (JOIN (JOIN (MERGE (SORT (ASSAY NATURAL),SORT (JOIN (JOIN
(PROFILE INDEX (XAK1PROFILE),PROFILEASSAY INDEX
(XAK1PROFILEASSAY)),ASSAYCATEGORY INDEX (RDB$PRIMARY2)))),SAMPLETYPE
INDEX (RDB$PRIMARY23)),JOIN (JOIN (JOIN (JOIN (JOIN (JOIN (JOIN
(SAMPLEGROUP INDEX (RDB$PRIMARY20),SAMPLE INDEX
(RDB$FOREIGN50)),SAMPLEORDER INDEX (XAK1SAMPLEORDER)),TESTREQUEST
INDEX (XIE1TESTREQUEST)),TEST INDEX (RDB$PRIMARY24)),RESULT INDEX
(XAK1RESULT)),UNIT INDEX (RDB$PRIMARY26)),PATIENT INDEX
(RDB$PRIMARY9))))

... ouch ... pretty complex! Unfortunately, Craigs Plananalyzer
reports an error about the plan.
Since I have no idea how to read the plan directly, I am a bit stuck
here.