XS_SCALE_MARKS_TO_FIT_LIMIT
Category in Advanced options dialog: Marking - parts
Use this advanced option to fit part marks as close as possible along the part they belong to by scaling the text height. Set the minimum scale with this advanced option.
Scaling works only with leader line options
Along line or leader line and 
Along line.
The default value is 1.0. This means that if you do not set the advanced option, Tekla Structures does not scale marks. Tekla Structures scales the text height in steps so that first it tries the scale of 0.9. If the mark does not fit, Tekla Structures scales the mark by 0.8, and so on.
This advanced option is model specific and the setting is saved in the options database.
Example
XS_SCALE_MARKS_TO_FIT_LIMIT=0.5