A 10mm change in the fork length will change the HTA by at least .5 degree and make a signiicant difference in the trail.

Trail is R/tanH - (offset/sinH). The first half of the equation is the trail without any fork offset and the second half is the reduction in trail due to the offset. An offset of only 38mm is on the small side to start with (makes for slow steering). You wouldn't generally want a lot less. You might want more to get a little quicker steering.

http://www.sheldonbrown.com/rinard/forklengths.htm