Do Open Invoice Reminders Use the Same HTML Wrapper as Tickets,Invoices,Estimates,etc.?

I am having a heck of a time getting my open invoice reminder html code to look right when being sent out to clients. Does it not use the HTML wrapper that invoices, tickets and estimates use? Why when I add code does some of the source code get removed/edited out?

To be less vague: When I copy the same source code from invoices and paste it into the “open invoice reminders”, the code changes and adds tons of “< br >” (breaks) and puts way too many spaces making the email format extremely wonky.

Anyone have any thoughts? Do I have to just copy the code from the HTML wrapper and then remove {{body}} with the code I put in Open Invoice Reminders?