Poll for WILDers: Concentration vs Accepting Imagery

I understand that WILDing is a very active/passive process. The active part is concentrating on the imagery, but you have to be passive enough to remain relaxed and allow imagery to occur.

So, how hard do you actually concentrate? Do you often slip into a non-lucid dream because you weren't concentrating enough? Or on the contrary, will unsuccessfully WILDing never lead directly into sleep (ie. you stop concentrating in order to fall asleep)

Thanks for your feedback!