Hi,
According to the comments in cam_ext.cfg,
So you could try to specify a different resolution for the text that the game will then upscale to the actual resolution being used for the game.; alternatively a fixed 2D resolution can be defined, which is aspect ratio corrected and scaled up
; to the current resolution, without enforcing pixel perfectness (ie. filtering makes it a bit less crisp)
For example if you're planning on playing the game at 3840 x 2160, then you may try:
d3d_disp_scaled_2d_overlay 1920 1080
It gave me some text that's smaller than when using d3d_disp_scaled_2d_overlay 64, but still larger than default.