It is possible your position is stunting its growth, or you have a small form of Gunnera. If the position is a bit dryish, a bit sunny, a bit short on lashings of fertility, Gunnera can be a bit insipid
The most impressive stands of Gunnera I came across where usually in valleys with high trees around them, unlimited well decomposed leaf compost, abundant moisture
You might look up photographs of the gardens of Heligan, Sheffield Park gardens, Hodnet Hall, to get some idea of how they like their feet in the shade and their heads in the sun...
http://www.americanponders.com/forum/in ... opic=349.0
~ A few from the Summer of '06 ~