I have the same scanner and love it. I use the contrast function and push it, then back down the brightness equally to normalize the lighting. The result is it makes the scan really sharp.

You can lock the sizing. I put a couple of black sharpie marks on the glass bed to indicate where i should place the chip, then i use the Zoom button instead of the preview. I've worked on ways to make it easier. The size I have locked at 41mm x 41 mm and also have the settings at 200 dpi 316x316.