dash vs. bash inconsistency

[Sasha Slijepcevic]

I am using Cygwin 3.1.4-1, bash 4.4.12-3 and dash 0.5.9.1-1.

I have a setup.exe in the root of my Cygwin installation, C:\cygwin64, for example.
If I set PATH=C:\cygwin64;C:\cygwin64\bin, I can run setup.exe from bash.

C:\>set PATH=C:\cygwin64;C:\cygwin64\bin

C:\>bash
$ echo $PATH
/:/usr/bin
$ setup-x86_64.exe  --version
Cygwin setup 2.903

However, in dash:
C:\>dash
$ echo $PATH
/:/usr/bin
$ setup-x86-64.exe --version
dash: 2: setup-x86-64.exe: not found

Am I misusing Cygwin trying to run executables from the top of the installation? Is it expected to all shells would behave the same?

Thanks,
Sasha Slijepcevic