Retinue & Dedicated Transport Confusion

[First_Among_Brothers]

I’m having a little bit of trouble figuring out the rules in this new edition--my apologies for the very simple question. How do I construct a retinue for a primarch and put it into a transport? So, let’s say I’m using Horus as my HQ. I choose a Justaerin squad as a retinue. I can use a Proteus as a dedicated transport, but apparently not a Spartan. But the squad size is 5 meaning that, unless the retinue option somehow allows me to take 4, I will have 6 models together with Horus that presumably won’t fit in the Proteus. Am I completely confused, here?

[Brother Kraskor]

Primarchs have Bulky (4), so Horus +5 Justaerin would not fit in a Proteus. However just because you can only take a Proteus for them as a Dedicated Transport, doesn't mean you can't take a Spartan in a Heavy Support slot, and then deploy the Justaerin inside. It just means you will need to use a Heavy slot for it instead of it sharing the slot with them. 

[Brother_Angelus]

A unit that buys a dedicated transport must start the game embarked on it. If they can't due to capacity issues, I don't know what that means. Presumably they can't select one they knowingly can't adhere to the rules for?

Edited November 1, 2022 by Brother_Angelus

[Gorgoff]

6 hours ago, Brother_Angelus said:

A unit that buys a dedicated transport must start the game embarked on it. If they can't due to capacity issues, I don't know what that means. Presumably they can't select one they knowingly can't adhere to the rules for?

Exactly.