Tiny fonts on dual external 2K (2560x1440) monitors connecting to 13 inch rMBP

Hi everyone,

I have been googling for a couple of hours but fruitless. Wonder if anyone experiencing the tiny system fonts when you connect rMBP to external 2K (2560x1440) monitors (I bought two Dell U2518D)?

At first I tried an HDMI cable from rMBP to one monitor but it could not output more than 1080p to the monitor. Then I tried a thunderbolt to Display port on external monitors. The resolutions go up to native (2560x1440) now. And the everything looks clear..... BUT the system font size is tiny all over the place. For example, the font size of tool bar on the top are so hard to read from normal office desk working distance.

I only found some articles online talking about selecting lower resolutions (say, 2048x....). That makes things larger but blurry. Also defeat the purpose of having a 2K monitor than regular 1080p ones.

Is there a solution to have both clarity and reasonably sized fonts on the external monitors?

Or Macbook pro is not supposed to working with external 2K or 4K monitors with decent font size?