Here's the link to the dtas manual: http://www.bayareaservice.com/Manuals/dats.pdf. I believe Fig. 2 shows the dtas installed in the bypass duct.
The HX is actually in the AHU, correct? If so, then the dtas is at least 3 feet or more from it.
Basically, the AHU is outside, the supply trunk starts out there, goes through the foundation and into the crawl space. Total length is about 6 feet - 3 feet outside, 3 feet in crawl space. (Rough estimates). On the crawl space portion of the trunk, the first thing installed into the top of the trunk (closest to the crawl space wall) are three ducts with zone dampers (I assume one is a shared zone since we only have two zones?)
Next in line is the dtas, which is installed on the side of the trunk. Then the bypass duct is installed in the same side of the trunk, about 1 foot from the dtas.
I know that's not a picture, but hope it helps visualize things. I will say that there doesn't appear to be any room before the zone ducts on the trunk to put the bypass duct, so it almost has to be after the zone ducts. My main concern there is whether that's acceptable or if it somehow reduce the efficacy of the bypass damper.
My next concern is that the dtas is both in LOS of the HX (although about 3 feet from it) and also installed AFTER the zone ducts. Again, does that reduce the efficacy of the dtas? If it's better to keep it after the zone ducts rather than before (since moving it before would move it at least a foot closer to the HX), should it stay where it is or would installing it in the bypass duct just before the damper be better since it would be out of the LOS?