Fscy on Aegisub doesn't appears on Avidemux

[TdT]

Hello everybody !

I'm translating videos, using the software Aegisub, saving .ass files. Thanks to that software, I can create cool effects easily, like extending the text when it's shouting for example. The tags to use this effect are {\fscx 200,\fscy 200)}. So it uses the scales x and y.

When I'm starting Avidemux to do the render, I'm barely touching the settings. My original video is already .mp4. I'm choosing MPEG-4 AVC -> Configurate. In : General, Encoding Mode, I'm changing Constant Rate Factor (Single Pass) to Average Bitrate (Two Pass). Movment, Motion Estimation Method, Exhaustive Search to 10.
Then in filters, I select my subtitles, choose them, and that's it.

When the rendering is going well, in the end, there is this matter : the subtitles, when the effect is used, only extend on the x scale, but not the y one. In other terms, it's just expending on the sides and not on the heights, which is really weird ! I don't know if it's something Avidemux can't handle or what, maybe I'm not choosing something in the settings, I don't even know.

So if someone can help me with that, it would be really appreciated !
Thanks to everyone aiming to help me.