Rhys, if I understand you correctly, you want the depth of field to cover subjects A and B. Is that correct?
Originally Posted by Rhys
If that's the case, the XT (and other models) have a mode called "A-Dep". This helps you control the depth of field automatically. Here is a quote from the XT manual:
A-DEP Automatic Depth-of-Field AE
This mode is for obtaining a wide depth of field automatically between a near subject and a far subject. It is effective for group photos and landscapes. The camera uses the seven AF-points to detect the nearest and farthest subjects to be in focus.
Does this information help you? The manual describes more in detail, how to use A-Dep.