iOS Mail - HTML Signature is wrong size - much smaller!

Hi all, I've seen a few old posts about this but couldn't see a resolution.

I'm trying to use a custom HTML signature for my work in Mail on my iPhone. It works perfectly on my mail app on my MBP and iMac but on the iPhone, it all shows as a fraction of the size it should be.

Anyone have any idea how to ensure the formatting is correct?

Have attached a couple of snapshots of it. These are screenshots of the incoming mail when sent from the different devices to mail on OSX. The first is the smaller one sent from iOS Mail and the second is the correct size sent from OSX Mail. (they both appear larger than they are in real life but I guess thats something to do with how the discussion format the images?)

[Image Edited by Moderator to Remove Personal Information]