c) Clearing the Wrists
Whatever handcuffing technique that you are using requires that you clear the wrists of any obstructions like clothing, watches, jewelry, etc..
Handcuffing over clothing cuffs is problematic for several reasons (the material can actually get caught inside of the handcuff and jam it up).
Also, the cuffs will not be as tight as they should be on the arrestee, so if the arrestee was to slide the cuff material away from underneath the applied handcuffs, he could possibly escape by slipping the cuffs off.
When placing on handcuffs on an arrestee in a rear, entwined bent-armlock, your forearm is parallel to his forearm, making the application of a handcuff difficult (i.e., the single strand must be fed through the overlapping forearms and wrists).