AutoCAD LT :: Importing Drawing As Block With Field References To Attribute Values

We have generic drawings of assemblies we use in layout drawings as standard details.  We insert them as blocks with one or two dimensions that vary (geometry remains the same-these are just representative for information). 

We could define these as attribute values so that a user types a length that displays in the drawing but if we wish this to be part of a dimension we would have to explode the dimension to manually replace the mtext dim value with an attribute tag.

This seems unsubtle so I edited the dim value to be a field referencing the attribute value and made the tag invisible.  This worked in the drawing-the attached shows the attribute tag ALL THREAD and the resultant dimension text (as a field value) replaced with the default value LENGTH.

When the drawing is inserted as a block it duly prompts for a value for ALLTHREAD and any value can be typed-`1200, 3500, 1672 etc. but the dimension does not update from the default value LENGTH, even after using attsync, regenall.  So, if the drawing recognizes the attribute then how come it cant recognize the graphic via a field reference and update it? Is it buried too deep in the database hierarchy for LT to make sense of it maybe?

I dont want to explode the dim but it looks like I may have too if this cannot be made to work.