There are several ways to change the size of blocks. Which method you use will depend on your specific needs. Some options:
First, make sure you're using the correct library for your standard. If you're using IEC symbols on a drawing that was set up for a western standard (NFPA or JIC), you may face some size issues, even with the feature scale multiplier.
In general, select 'Inch' if you're using a western standard, and select 'mm Full Size' if you're drawing in IEC. I believe that the 'Inch Scaled To mm' is for bringing metric symbols into a non-metric drawing...but don't quote me on that. Even ACADE Help doesn't explain that one.
You can scale all blocks that you insert from the Icon Menu, there's a 'Scale Schematic' field at the bottom of the dialog. I've never had to use it, so not sure if you have to re-select it every time you open up the dialog.
You can change the actual size of an entire symbol library with the 'Modify Symbol Library' tool. It is found under Schematic>Other Tools>Symbol Builder pull-down. NOTE: back up your libraries before doing this. Also, go into the command already knowing what scale factor to change the symbols by...this command takes a long time to run, you don't want to have to do it more than once.
Hope this helps,
Jim

Jim Seefeldt
Electrical Engineering Technician