Unlike Verilog-D, Verilog-A has "system" include files for default/standard disciplines physical constant values and maybe simulator/tool supported features. As with "C" Verilog-A[MS] should include these with "<>" rather than '"' quotes.
For backward compatibility the system file include path should be appended to the end of the user search path so that system files quoted with '"' will be found (if not overridden).