I usually encounter the change in icon size after I remotely control my office PC from my Surface Pro 4, which is extended to an 1080p external monitor. Is there an option to switch the icons back to the small icons as in the default view? I'm using commander view btw.
Can you give us step-by-step instructions to reproducing the problem?
Do you remotely login while WinSCP is running? Does WinSCP keep the large icons even after you close it and start it while logged in locally?