While there are different opinions on using them I recommend leaving LTSCALE, PSLTSCALE, & MSLTSCALE system variables all set at 1 their default. Then set the Annotation Scale for the Model tab the same as you're using in your Layout Viewports so the linework is displayed the same in both places.
Of course it only works if the template you're using is set up correctly. Check your MEASUREINIT and MEASUREMENT system variables as there are separate lin files for Imperial and Metric.