Well, it seems a better idea is to cut the steerer 10-15mm above where I think the final cut will be, insert the plug, and use spacers to position the stem. Clamp it down and check the fit. Move spacers from below to above the stem to lower it and repeat until the fit is good. Then allow for a 5mm spacer above the stem, and cut the steerer 1-2mm short of the top spacer to allow for the compression cap.