[QUESTION] New to design. Need help with bleed size.

Hopefully I'm not posting this in the wrong sub.

I recently designed some posters for my band, but I designed them for A2 but will be printing them on A3. I'm about to add bleed marks, and was going to make them 3mm. With the downscaling of the image when printed, would I need to upsize the bleed marks to 6mm so it's 3mm when placed on A3 paper?

I'm doing this in photoshop so I'll be adding the bleed manually, then upsizing the canvas to SRA2 size, ready for print.

I've searched everywhere online to no avail. Any help would be very much appreciated.

Great design resource

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