Confused about flash units for R5 Mk 2

[pedz]

According to this page, I can use my Macro Twin Lite MT-26EX-RT but I can not use my Speedlite EL-1 without the Multi-Function Shoe Adapter AD-E1 (which is back ordered at B&H 😢).

I don't understand this.  Can someone explain why this is true?

The electrical connections on shoe on the flashes looked the same to me.  The only difference I can see if the how the rubber boot is slightly different.  The EL-1 physical fits on the camera but I haven't turned it on.

[deebatman316]

The speedlite will not fully slide into the hot shoe and communicate with the camera. Causing the flash not to communicate properly with the camera.

[p4pictures]

The rubber seal around the foot of the EL-1 does not fit the shoe of the R5 Mk2 and this means it is not possible to fully engage the clamp to hold the flash on the hotshoe. 

You have two options, use the AD-E1 adapter, or remove the rubber seal from the EL-1. It will pull off quite easily and is easy to reattach too.