I just posted a complaint to this issue here: http://www.apple.com/feedback/iphone.html
It appears Apple has programmed Siri to limit text sizes, and this is severely hampering its usability and the usability of my phone. If I try to use Siri to send a text that is a few sentences long, I get an insulting response from Siri (that I suppose is supposed to be witty) telling me to reduce the sentence size. Come on guys. This is such an unforced error by you.
I like to send texts via Siri when I am doing other things: cooking, cleaning, working with my hands around the house, feeding my son, etc. This multi-tasking is quite important in allowing me to get done the things I need to. I am extremely busy working full time and caring for a cognitively impaired special needs son.
By limiting my text sizes through Siri, you have rendered it useless for this purpose, which impacts my time. You are pushing away a customer here. I've had iphones for several years, but Samsung makes some great products now, and this move has caused me to begin shopping for a new phone from someone other than Apple.
Not incidentally, having Siri recite back a very long response when I try to send a text of just a few sentences compounds the error. It is anger inducing. It's bad enough you have limited the functionality of the phone, but to have Siri rattle off some esoteric quote to prove the point is a thumb in the eye of your customers.
There is a thread on this that you can find here: https://discussions.apple.com/thread/5015216?start=0&tstart=0