Size independent of placement in patcher

Hello,

I tried for several days and was looking for a solution but didn't find. However it looks like a simple issue.

I am using patching_rect message to a slider. It requires four arguments in a specific order: X-coord in patcher window, Y-coord in patcher window, width and height.

Here's the question: how to modify only the last argument without having to know the previous values?

At all times I have to include X and Y coords, however I am not interested in looking for their values (it makes my patcher excessively complicated).

Greetings from Poland!