I did the same - chain measured & should have fitted using the maths - but way too slack, so I nipped out a couple of links (i.e 1M 1F) and now fine!
I think the arguments over 'accidental' big/big gear use are becoming somewhat redundant these days though surely, with the proliferation of 1x9 & 1x10 drivetrains, you may well end up in big/big - which is the same as small/big if you've only got one ring up front and haven't changed to a shorter-cage mech..
2013 On One Scandal | 2011 Ghost ASX 3700 | 2008 Magura Test Bike | 2006 Raleigh RS950
1999 Voodoo Hoodoo | 1999 Raleigh RSP 450 | 1997 Giant ATX-D 990 | 1997 Ghost X-700
1995 Giant Cadex MCM-3 | 1995 Voss Ti | 1993 Giant Cadex CFM-2 | 1992 RS Topline Mammoth