Digital BW, The Print

Hi,
I'm about to have an exhibition and am wondering whether I should get my glossy (swellable) HP paper stuck down.

The strange thing is that I have some 4.5x6" prints on A5 paper matted and framed in my living room and a slight ripple can be seen (just). 

However, I have an A4 print (all these are on HP swellable paper with Formacote backing), matted and framed, behind the sofa, after not selling at a previous exhibition. 

Although the bigger one should be more prone to curling, it is the only one that has not observably curled, of the mentioned prints.

What is happening here?

So ... A4, is sticking down all that important? 

thanks,
Richard
--
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