Between the 2001 and 2011 census the number of english born people living in Wales(all ages) rose by 46k.
By 2018 the total estimated population increase of all people living in Wales regardless of nationality rose by 76k from the 2011 census figure.
In 2019 259k more people over 18 voted Conservative than did so in 2005.
There has been a massive swing in that period from Labour to Conservative that cannot be attributed to English immigrants even if every immigrant since 2001 voted Tory and the population increase since 2011 is solely due to English immigrants of voting age.
I'd find some other justification to enhance the Welsh side of Offa's Dyke.