Using srcset via Kirby Query Language (kql plugin)

I’m using the kql plugin to get to the API Endpoints. My question: is there a way to use the full power of the srcset file method? The following code works well – but, if I want to use the more complex sizes options (f.ex. '400w' => ['width' => 400, 'format' => 'webp']) it returns the original image url with an empty sizes attribute. If possible, how do I have to write it in query language? Thanks for any help!

image: { query: "structureItem.img.toFile", select: { id: true, filename: true, url: true, srcset: "file.srcset([300,800])" } }