if you have a lower wattage C.H.E. in a large viv. it will spend all day/night running.. and cost you more in the long run
place a 250w C.H.E in a 2x1x1 it will only run for short periods of time.. the bigger heaters take longer to cool down. so your viv will stay warmer for longer before the ceramic has to kick in again
Ideally place a larger ceramic on a pulse prop stat... they only apply a little bit of power to "top up" the heater but cost a few pennies more .. ( but think of the cost saving on the elec bill )
you could use a dimming stat but you will be running the ceramic for longer periods just at a lower power level.
RFUK, better than the arguments on Jeremy Kyle