org-agenda-entry-text-maxlines

org-agenda-entry-text-maxlines is a variable defined in `org-agenda.el'.
Its value is

5

Documentation:
Number of text lines to be added when `E' is pressed in the agenda.

Note that this variable only used during agenda display. Add add entry text
when exporting the agenda, configure the variable
`org-agenda-add-entry-ext-maxlines'.

You can customize this variable.