yes - they fit in the footwell of Elises
Ive seen a couple of cars go up in flames on trackdays and the small extinguisher I have in my Elise (like yourse) is only really good for helping others get out of their vehicle (at a push) ...only a plumbed in 5L + jobbie will have a chance of putting out a real engine bay fire etc
when you see how fast they go up once a fire has started you wont be worrying about extinguishers ...just getting out and running away ! ....if you are really worried, get yourself some Nomex underwear, race suit, boots, gloves and make sure you have a proper fireproof car helmet i.e not a motorbike one for road use