Samsung Galaxy Note 4 — Spen for writing messages - input area

Hi,
Have had my note for about 2 weeks now, loving it. Am now starting to use the S pen for most things including writing text messages, but one thing is confusing me. Most times when I go to write, the input area appears at the bottom of the screen and takes up about 1 third of the screen and is "1 line at a time", but occasionally, for no reason I can spot, the input area becomes full screen and I can write multiple lines of text. It is quite strange because I have written 2 texts pretty much one straight after the other and the first went into "full screen" handwriting mode, the second went into the more frequent "1/3 screen, 1 line at a time mode." I quite like the full screen option, could someone tell me how to toggle or set this option so it is the default?

— modified on Apr 22, 2015, 11:59:10 AM