Difference between 还/更 in comparasion phrases
Both 还 and 更 have more than one meanings and the meaning of &quot;even more&quot; is overlapped between the two characters,
When it means  &quot;even more&quot; the two characters are interchangeable.

Yao Ming 比 Michael Jordan 高 = Yao Ming is taller than Michael
(It would be true even if Yao Ming was 5'3&quot; and  Michael Jordan was only 5'2&quot;)

~

Yao Ming 比 Michael Jordan 更/还高 = Yao Ming is even taller than Michael
(It would be true only if Michael Jordan was considered very tall)

~

她比 Megan Fox 漂亮 = she is more beautiful than Megan Fox
(it would be true even if she was just less ugly than Megan Fox)

~

她 比 Megan Fox 更/还漂亮 = she is even more beautiful than Megan Fox
(It would be true only if Megan Fox was considered very beautiful)

[比 (N) 还 (adj)] = [比 (N) 还要 (adj)]
[比 (N) 更 (adj)] = [比 (N) 更加 (adj)]