I can set the full resolution of 3440 x 1440, when using Version 1.16.
It is available in the options menu.
But when using Version 1.15, resolution seems to be limited to 1920 x 1200 on my machine.
I think, EECH V 1.15 supports only DirectX 7, which is limited to 2048 x 1536 maximum.
V 1.16 supports DirectX 9(at least partially), which allows higher resolutions.