I think we are using differing methods.
I am not doing above.
For example when I added the CbsSetupDxe from ZEA to C7H UEFI I do this:-
i) Open ZEA UEFI in UEFITool, search for GUID F639D37E-, click the found message so browser window takes me there, expand the GUID, select PE32 and extract as is.
ii) Open another UEFITool, open C7H UEFI, search for GUID A5E369C8-, click the found message so browser window takes me there, expand the GUID, select PE32 and replace as is with the ZEA CbsSetupDxe.
The file will be correct size, will flash using flashback.
When I was modding CbsSetupDxe I was again extracting it only and placing it back after edits, again UEFI size was correct.
UBU updates also keeps same file size, so file will flash using flashback.
*** edit ***
You may recall I was trying to change UEFI version string.
If I changed via HxD file would not flash. If I changed via BCP secure capsule signature lost. The way to do it is using UEFITool, extract as is GUID AB56DC60-, edit in HxD, replace as is. File can be flashed using flashback, etc.
C7H WiFi 2304.1 download link
i) UEFI/AGESA version mod
ii) CPU mCode & others elements updated via UBU