My way no need, but if you want also can... but you have to dismantle the whole fender because applying Flex Mat you need to apply pressure for better contact.

Dampening Mat is not suitable for vertical application, even though it is butlyn too.

My way I choose Suppression Pads over Flex Mat for the ease of application, to obtain the same result/effect.

Are we talking about Myvi or other cars?

Suppression Pads, cut and paste. Stick it to the metal body part of the fender. Paste it at the area where you think it can reduce the vibration more.
Normally I stick it close together, to achieve better results.
Which part of Wira a/b that you would like to soundproof? I try not to install for you, can you D-I-Y instead?    Heheheh... cheaper ma.