IDS 9.21
Have got 2 temp dbspaces defined :
DBSPACETEMP dbstemp,dbstemp2 # Default temp dbspaces

onstat -g iof
gfd pathname totalops dskread dskwrite io/s
3 /disk05/rootdbs 34 21 13 0.0
4 /disk02/dbstemp 98 96 2 0.1
5 /disk03/dbstemp2 4312 4310 2 5.8
6 /disk01/albdbs 9452 9440 12 12.8
7 /albdbs2 8667 8667 0 11.7
8 /disk04/logdbs01 4 3 1 0.0
onstat -d
Dbspaces
address number flags fchunk nchunks flags owner name
25ba47d0 1 0x1 1 1 N informix rootdbs
25be3c08 2 0x2001 2 1 N T informix dbstemp
25be3d50 3 0x2001 3 1 N T informix dbstemp2
25be3e98 4 0x1 4 1 N informix albdbs
25ba4a80 5 0x1 5 1 N informix albdbs2
25ba4bc8 6 0x1 6 1 N informix logdbs
6 active, 2047 maximum

Chunks
address chk/dbs offset size free bpages flags pathname
25ba4918 1 1 0 1000000 994722 PO- /disk05/rootdbs
25be3500 2 2 0 500000 499859 PO- /disk02/dbstemp
25be3668 3 3 0 500000 495315 PO- /disk03/dbstemp2
25be37d0 4 4 0 750000 500867 PO- /disk01/albdbs
25be3938 5 5 0 750000 641228 PO- /albdbs2
25be3aa0 6 6 0 1000000 99947 PO- /disk04/logdbs01
6 active, 2047 maximum

Dbaccess/update statistics DOES use both temp dbspaces but user
programs do NOT. Why ?
(albdbs = ANSI logging, select .... order by ... )

Thanks
Roger While

Normally the user programs should use the temporary dbspaces for sorts, group by, temp indexes and stuff.
Programs like access for example tend to ask for the whole table (select *) and do the sort on the client machine. In that case, no temp space is used.
You could trace your communication between client/server to check your SQL statements.

Or you could try and set a pdq priority to prioritize parallellisme.