upPrev box not appear when i want & i cant configure size of image and excerpts

Hello,

I use upPrev.
I find it works very poorly for this moment … If you can help me to fix that this would be very nice to you.

In the setting I set to “décalage (in french) or timing delay???”(portion size of the page to scroll (in percentage) required to bring up the box.)”: 40%
I currently have only 3 items on my blog that is still new.
Well this setting only works for one of these items. For the other 2 upPrev box appears only when the cursor reaches the bottom of the page with the comments. So those who do not read the comments will never see the box appear …

More I can display excerpts and images associated items in the up prev box by checking the boxes corresponding, but I can’t configure the width of the image and the number of words of the excerpts which ignores information that I put in the boxes.
What can I do?

http://wordpress.org/extend/plugins/upprev-nytimes-style-next-post-jquery-animated-fly-in-button/