Just put some 16" wheels on my 2.0 with winter tyres.

The tyre pressure sticker inside the fuel flap states R16 should be 230 front and 270 rear

270? That seems way more than any other tyre - is that right? Some 18" are 210 front and back

My 1.6d Estate says 230/230 for "normal load" and 250/320 for "Full load", if running 205/55 R16.  That is higher than the R17 I have - the sticker says 220/220 and 250/300 for those, so the pressures are lower - as you have noted with your 18's. 18's would be 210/220 and 260/310 according to my estate's sticker. 

 

So - the hatch (your sig shows your 2.0 is one of those) doesn't need as high a pressure on the rears with full load, so I'd say your sticker is right.