Spheres of Might: Deflecting Shield

GM who is moving from PF2E to Spheres PF1E and I have a question about the Shield Talent Deflecting Shield, which reads as follows:

“Your shield bonus to AC applies against touch attacks.”

One of my players is a Blacksmith who is focusing on tower shields and sundering enemy equipment. He has taken the Deflecting Shield talent and has a +1 enhancement bonus on his tower shield. If a tower shield has a base shield bonus of +4, would Deflecting Shield increase his touch AC by 4 or 5? In other words, does an enhancement bonus increase the value of the bonus it is “enhancing”, or is it a separate type of bonus?

Any help would be appreciated! And if you have any tips of things I should know about running PF1E, Spheres or otherwise, I’d appreciate that too.