How to force a certain file into context!

Hello everyone! It seems that each time I @ a file in chat, it offers it to LLM for its tool to ask for it and read a portion of it. With the models like 2.5 pro and o3 I routinely just include large files into their context if I so wish (in their web ui), because I know they work with information better that way (they don’t have to guess what to query for and work with that limitation). So the question is, do I even have an option of doing that as a power user?