documentation https://www.zabbix.com/documentation/current/manual/config/items/itemtypes/zabbix_agent isn't inaccurate at the point for the "system.swap.size" in relation to the -ZBX-8809- 

Because the documentation mentions only the percentage:

"Note that this key might report incorrect percentage on virtualized (VMware ESXi, VirtualBox) Windows platforms. In this case use perf_counter[\700(_Total)\702] key to obtain correct swap usage data."

However, if you check the -ZBX-8809-, there is also non-percentage metric 'system.swap.size[,free]' affected.

I think that documentation example should be clean that the perf counter is in percentage.
And it should be clean that all <type> are affected in such conditions.