Does anyone else have these issues?

I have put an MS13 in the downstairs wc and a AMW2 behind the switch. When I read the MS13 literature it said that it will turn off x minutes after detecting movement.
I took this literally and assumed that it meant x minutes after it's last detection of movement. What it acually does is turn off 1 minute after it FIRST detects movement!
Are there any other X10 sensors that will actually do a proper job or is there a setting I should be changing?

Also I have a MS13 on the upstairs landing, and I can walk from one bedroom to another and it will fail to trigger. And then when I walk back it triggers. Has anyone any expeience of these 'missing'?

Any help or shared experience would be appreciated.

frank