I was inspired to try to make larger font sizes for 4K monitors with the Large UI size when I saw this post in the Steam forums.  I also have a 4K monitor, use the large UI size and sometimes wish the fonts were a little larger.  The comment by Yarlen showed me that it should be easy to make the fonts larger but that it could cause other problems.  I decided to try anyway.

I tried with several large increases in font size first and got bad results.  The first acceptable result came with a 25% increase in font size.  There were still problems in some areas, but I felt that size might be acceptable even with the problems.  An increase of 20% was better with fewer problems.  An increase of 15% was even better.  There were just a few problems, but the text was beginning to get smaller than I would like.  I did not try any increase that was less than 15%.

I learned there are three types of areas where text appears in the game, and the increase in text size can cause different problems or may not cause any.

Area #1
These areas have already been designed for text larger than the area, so a scroll bar appears when the amount of text takes up more space than the base size of the area.  The text automatically uses word wrap to fit in the area.  The increases in font size did not cause a problem that I found.

Area #2
These areas are usually a tool tip that is designed to have a fixed width with the height automatically adjusted to fit the amount of text it contains.  I did not find a problem with any of these, but there was one case where the height of the area was almost the same as the height of the display.  If there is a case where there is more text, I expect the area to continue past the bottom of the screen with no way to see the bottom part of the text.  This is how the tool tip for Ascension Crystals displays when there are a lot of crystals in a galaxy.

Area #3
These areas have a fixed size that never changes.  They are designed to fit text of an expected size.  Buttons are like this, but there are other areas with the same design.  There were a lot of problems with these.  Some have the right part of the text just fade out.  This is how it normally works in the game for the default text in any UI and screen resolution when the text in longer than the space available, so increasing the font size doesn't make a difference in this case.  Some don't have the text fade out, so it continues to the right and overlaps whatever is to the right of the area.  Other areas don't let the text continue to the right, so the text uses word wrap to try to fit in the area.  This is how buttons usually work.  The result is that only the bottom part of the first line of text is visible at the top of the area, and only the top part of the second line of text is visible at the bottom of the area.  Anything after the second line of text is lost.

I feel that the 15% increase in size is best for me.  Others may still want a larger size, so I have mods for increases of 15%, 20% and 25% so the preferred size can be determined by each user.  Only one should be used at a time.  Using more than one at time could cause strange results.  The changes in modded FontSizes.xml files are all in the last part of the file.  All my changes have a comment about what change was made and the original value before the change.  You are welcome to make your own changes to fit your preferences.


IMPORTANT NOTE
All of these mods work with saved games, so use a save to determine which mod you like best.  Be sure to check multiple screens to see how the mods change the way the text appears.


Here are the names of the mods
OS 4K 15 Font Size Mod
OS 4K 20 Font Size Mod
OS 4K 25 Font Size Mod


OS stands for Old-Spider
The 15, 20 and 25 stand for the % increase in font size.

All of them are available in one zip file here.