Ubuntu 18.04 处理 4k 外接显示器

我的 PC 上有一个 Ubuntu 18.04，我想使用我的外接显示器。它是支持 4K 显示的 LG UltraFine 27UL850-W。但是，当我插入它时，与笔记本电脑的主屏幕相比，它似乎被缩小了。

以下是输出xrandr：eDP-1-1 是我的笔记本电脑屏幕，DP-1-1 是我的外接显示器。

Screen 0: minimum 8 x 8, current 5760 x 2160, maximum 16384 x 16384
eDP-1-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 381mm x 214mm
   1920x1080     60.01*+  60.01    59.97    59.96    59.93    40.00  
   1680x1050     59.95    59.88  
   1600x1024     60.17  
   1400x1050     59.98  
   1600x900      59.99    59.94    59.95    59.82  
   1280x1024     60.02  
   1440x900      59.89  
   1400x900      59.96    59.88  
   1280x960      60.00  
   1440x810      60.00    59.97  
   1368x768      59.88    59.85  
   1360x768      59.80    59.96  
   1280x800      59.99    59.97    59.81    59.91  
   1152x864      60.00  
   1280x720      60.00    59.99    59.86    59.74  
   1024x768      60.04    60.00  
   960x720       60.00  
   928x696       60.05  
   896x672       60.01  
   1024x576      59.95    59.96    59.90    59.82  
   960x600       59.93    60.00  
   960x540       59.96    59.99    59.63    59.82  
   800x600       60.00    60.32    56.25  
   840x525       60.01    59.88  
   864x486       59.92    59.57  
   800x512       60.17  
   700x525       59.98  
   800x450       59.95    59.82  
   640x512       60.02  
   720x450       59.89  
   700x450       59.96    59.88  
   640x480       60.00    59.94  
   720x405       59.51    58.99  
   684x384       59.88    59.85  
   680x384       59.80    59.96  
   640x400       59.88    59.98  
   576x432       60.06  
   640x360       59.86    59.83    59.84    59.32  
   512x384       60.00  
   512x288       60.00    59.92  
   480x270       59.63    59.82  
   400x300       60.32    56.34  
   432x243       59.92    59.57  
   320x240       60.05  
   360x202       59.51    59.13  
   320x180       59.84    59.32  
HDMI-1-1 disconnected (normal left inverted right x axis y axis)
DP-1-1 connected primary 3840x2160+1920+0 (normal left inverted right x axis y axis) 600mm x 340mm
   3840x2160     60.00*+  30.00  
   2560x1440     59.95  
   1920x1080     60.00    59.94  
   1600x900      60.00  
   1280x1024     60.02  
   1280x800      59.81  
   1152x864      59.97  
   1280x720      60.00    59.94  
   1024x768      60.00  
   800x600       60.32  
   720x480       60.00    59.94  
   640x480       60.00    59.94  
HDMI-1-2 disconnected (normal left inverted right x axis y axis)

我怎样才能将它缩放到一个不错的分辨率而不会模糊？我想我的外部显示器需要 150% 的比例，以便一切看起来都很好。