It is impossible to alter the size of a checkbox from the default. Altering the control size does not increase of shrink the size of the checkbox itself.
I can confirm with Version: 18.104.22.168.alpha0+
Build ID: 7f476fea47f06a7f8cc961dd4f6595a524346fa5
TinderBox: Linux-rpm_deb-x86_64@46-TDF, Branch:master, Time: 2014-12-27_23:36:28
inherited from OOo -> https://issues.apache.org/ooo/show_bug.cgi?id=26593
Adding self to CC if not already on
This bug has been around for 11 years in Oo, is there any chance it may be picked up and fixed in LO?