Have you ever had a block be the wrong size when you insert it with a scaling factor of 1?

The easiest way to determine if the block insertion units are compatible with the units of your drawing is to highlight the block after it is inserted, too small or large, and open the Properties palette. Scroll to the bottom Misc section and look at the Block Unit listing. Does the listing match your units or is it Unitless?  If not, you will need to Wblock the block out of your drawing, resize it correctly to your units, and then change the Insert Units to Unitless in the new file.

 Now, when you reinsert the block, the definition will be the correct size and should replace the existing blocks to be the same size.