I've found most of our males seem less inclined to lock up when in shed so we just don't bother and let them get it over with first. I have been told, however, that if the female is in shed it's often a good time to put the male in as she's not likely to be overly active and move away from his advances at that time. I've also been told you can use very fresh male sheds to trigger breeding activities by either placing it into a potential female mates enclosure so she smells an adult male close by or into another breeding tub where that male isn't doing his thing. Apparently it can make him more interested in breeding that female because he thinks he smells another male horning in on his action.